I. INTRODUCTION
The classic international law doctrine of ‘intervention by invitation’, and its problematic application in times of grave internal turmoil, has (re-)gained traction in recent years. This is due to several instances of State practice, including the French intervention in Mali (2013), the Russian intervention in Ukraine (2014) and the US-led military operations against ‘Islamic State’ in Iraqi territory. The most recent illustration concerns the crisis in the Republic of Yemen, where, in late March 2015, the internationally recognized President-in-distress requested military assistance from neighbouring countries to quell an armed insurrection, a matter of days before fleeing the country. An intense Saudi-led aerial campaign, combined with a crippling naval blockade, started soon after. It received political and material support from several States, which notably included Western powers.
Although it received no prior fiat from the UN Security Council and took place against the background of a civil war, the operation met with approval, or at least acquiescence, from a considerable number of States, with only few critical voices. Closer legal scrutiny of the operation was virtually absent at the level of the international community. This article provides an in-depth overview of the legality and legal implications of the Saudi-led intervention, by, first, setting out the factual background (section II) and the reaction of the international community (section III). Next, we critically examine two possible legal justifications for the use of force on Yemeni soil. First, having regard to the arguments put forward by the intervening States, section IV discusses whether Saudi Arabia and its coalition of the willing could invoke the right to self-defence (individual or collective) against the rebel ‘aggression’. Second, section V considers whether President Hadi could validly request or consent to the use of armed force for the purpose of restoring his government to power. Finally, Section VI sets out some tentative conclusions and assesses the case's precedential value.
II. FACTUAL BACKGROUND TO THE YEMENI CRISIS
On 26 March 2015, a multinational coalition led by Saudi Arabia and backed by logistical and intelligence support from the United States and the United Kingdom launched ‘Operation Decisive Storm’ on the territory of the Republic of Yemen. The assault was to be ‘limited in nature’ and was allegedly ‘designed to protect the people of Yemen and its legitimate government from a takeover by the [Houthi rebels]’.Footnote 1 It was undertaken pursuant to a ‘direct request’ from the embattled Yemeni President Abdo Rabbo Mansour Hadi two days earlierFootnote 2 and was set in motion following Hadi's flight from the southern port city of Aden to the Saudi capital of Riyadh in the face of advancing rebel forces.Footnote 3
The Houthi armed insurrection, which triggered the Saudi-led intervention, was the result of a long prelude dating back to early 2011. At that time, inspired by ‘Arab Spring’ revolts, popular protest erupted in Yemen, calling for long-time strongman president Ali Abdullah Saleh's resignation.Footnote 4 Slowly but surely, the peaceful popular demonstrations were transformed into a complex, violent conflict between armed (tribal) militias and internecine government troops.Footnote 5
In April 2011, negotiations under the auspices of the Gulf Cooperation Council (GCC), the United Nations (UN) and the European Union (EU) resulted in the GCC Initiative on Yemen and a complementary set of implementation mechanisms.Footnote 6 In November 2011, President Saleh agreed to sign the initiative,Footnote 7 which envisioned a two-phased transition period. Its first phase resulted in a power transfer from Saleh to vice-president Hadi. The latter was put forward as the sole consensus candidate for the presidential elections on 21 February 2012, where he received a substantial mandate from the Yemeni people, although both the Houthi and Southern movement called for a boycott.Footnote 8 The elections formally signalled the start of phase two, a two-year timeframe during which the priorities were convening a Conference for National Dialogue (NDC) and hosting general elections by early 2014.
It took well over a year for the National Dialogue Conference to start in March 2013. An Outcome Document containing nearly 1,800 recommendations was finally released in January 2014Footnote 9 and the UN Security Council adopted resolution 2140 in support of the transition process, imposing an asset freeze and travel ban for individuals ‘engaging in or providing support for acts that threaten the peace, security or stability of Yemen’.Footnote 10 Finally, a few weeks after the official closure of negotiations, a small committee, handpicked by Hadi, decided that Yemen would become a six-region federation.Footnote 11
Following the end of the NDC proceedings, the Houthi movement, disturbed by the prospect of a six-region federal State structure, continued its fight against ‘Saleh-era power centres’,Footnote 12 and in March 2014, embarked on a successful campaign of territorial expansion.Footnote 13 The movement, also referred to as Ansar Allah (‘Supporters of God’), has its origins in the protection of Zaydi traditions, an offshoot of Shi'a Islam, against ‘political exclusion and marginalization’.Footnote 14 Led by the Al-Houthi family, it fought on six separate occasions against Yemeni government forces, with hostilities formally ending in 2010. Curiously, its territorial gains after March 2014 were due to a ‘coalition of convenience’ with forces loyal to their former arch enemy, notably the deposed president Saleh.Footnote 15
On 30 July 2014, the Yemeni government substantially raised the prices for gasoline and diesel.Footnote 16 The measure infuriated Yemenis and led to mass protests, endorsed by the increasingly visible Abdulmalik Al-Houthi. The Houthis set up camps and checkpoints in and around the capital Sana'a, exerting pressure on the government to repeal this measure and demanding the formation of a more inclusive government.Footnote 17 By the end of September, and again with the cooperation of Saleh loyalist troops, Houthi militants had taken full control of the capital.Footnote 18 On 21 September 2014, the Peace and National Partnership Agreement was signed, which gave in to all Houthi demands,Footnote 19 resulting in the formation of a new government by mid-December.
Early 2015, the situation deteriorated further. President Hadi and members of his cabinet were put under house arrest and collectively resigned.Footnote 20 On 6 February, the Houthis finalized their coup d’état by releasing a ‘constitutional declaration’ dissolving Parliament and establishing a five-member presidential council and a supreme revolutionary committee.Footnote 21 The UN Security Council responded by demanding that the Houthis unconditionally return to the negotiating table, release all individuals under house arrest and withdraw their forces from government and security institutions.Footnote 22 A week later, Hadi escaped from house arrest and fled to the southern city of Aden. He released a statement appearing to rescind his resignation and declared Aden as Yemen's temporary capital.
The violence in Yemen continued to spiral out of control. Islamic State gruesomely announced its presence in Yemen by attacking two Shi'ite mosques in Sana'a.Footnote 23 Additionally, rebel forces continued their march on Aden. Faced with a rapid Houthi advance, Hadi requested military assistance and fled to Riyadh.Footnote 24 On 26 March, Operation Decisive Storm was launched, led by Saudi Arabia, but receiving support from several other GCC and Arab countries.Footnote 25 Only Egypt, Sudan and Senegal declared a willingness to engage ground troops, while other States pledged deployment of up to 30 fighter jets.Footnote 26 Egypt furthermore declared naval support, while the US and UK offered logistical and intelligence support.Footnote 27 Finally, Somalia consented to the use of territory, air space and ports for coalition purposes.Footnote 28
The operation formally lasted until 22 April 2015, after which the military objectives were allegedly achieved, and Operation ‘Renewal of Hope’ began. This second operation purportedly shifted focus to ‘the political process that will lead to a stable and secure future of Yemen’,Footnote 29 but was, however, not fundamentally different from Decisive Storm, in the sense that bombardments of Houthi strongholds continued largely unabated.Footnote 30 A five-day humanitarian ceasefire was agreed on 12 May 2015, but hostilities resumed within hours of its expiration.Footnote 31 The present article was finalized at a time when hostilities were still ongoing, with little hope for a diplomatic breakthrough in the immediate future.Footnote 32
III. REACTION BY THE INTERNATIONAL COMMUNITY
Coinciding with the launch of Operation Decisive Storm, Saudi Arabia, the United Arab Emirates, Bahrain, Qatar and KuwaitFootnote 33 submitted a joint statement to the UN Security Council explaining the justification for the military operation.Footnote 34 The statement begins by citing a letter written by president Hadi on 24 March 2015 in which he sketches the disastrous situation in his country. Hadi's letter repeatedly refers to ‘ongoing acts of aggression’ by the ‘Houthi coup orchestrators’, which are said to undermine Yemen's security and stability. At the same time, reference is made to militias ‘being supported by regional Powers that are seeking to impose their control over the country and turn it into a tool by which they can extend their influence in the region’, thus also threatening the security of the entire region. The letter subsequently proceeds to request for assistance:
I urge you, in accordance with the right of self-defence set forth in Article 51 of the Charter of the United Nations, and with the Charter of the League of Arab States and the Treaty on Joint Defence, to provide immediate support in every form and take the necessary measures, including military intervention, to protect Yemen and its people from the ongoing Houthi aggression, repel the attack that is expected at any moment on Aden and the other cities of the South, and help Yemen to confront Al-Qaida and Islamic State in Iraq and the Levant.Footnote 35
The remainder of the letter of the five Gulf countries spells out a variety of justifications for the operation. Thus, reference is again made to Hadi's request ‘for immediate support’ to protect Yemen ‘from the aggression of the Houthi militias’. It is emphasized that the Houthi militias are ‘supported by regional forces’ seeking control over Yemen in order to use the country as a base from which to influence the region. In addition, it is observed that ‘President Hadi has also appealed for help in confronting terrorist organizations.’ The statement subsequently shifts emphasis to the threat posed by the Houthi militias to Saudi Arabia. It depicts ‘the presence of heavy weapons and short and long-range missiles beyond the control of the legitimate authorities’ as a ‘grave and ongoing threat to our countries’. More specifically, it warns of an attack against Saudi Arabia, as the Houthis ‘have already carried out a bare-faced and unjustified attack on the territory of Saudi Arabia, in November 2009, and their current actions make it clear that they intend to do so again’.Footnote 36
While the statement of the five Gulf countries invokes multiple grounds, and does not expressly refer to Article 51 UN Charter and/or the right of self-defence, the latter legal basis, and in particular the right of collective self-defence, seems to be at the core of the legal justification put forward by the intervening States. Such a reading is supported by a statement made by the (then) Saudi ambassador to the United States that same day, asserting that ‘President Hadi requested on the basis of Article 51 of the U.N. Charter, the assistance and support by all means necessary including force . . . . He has also based his decision on the Arab League Charter's collective self-defence mechanism.’Footnote 37
At a summit of the Arab League, Arab leaders approved of the operation, affirming that its legality was based upon the triad of treaties invoked by Hadi, notably the Arab Treaty of Joint Defense,Footnote 38 the Arab League Charter (Article 6), and Article 51 UN Charter.Footnote 39 The United States provided logistical and intelligence support, thus clearly approving of the course of action as well. In a statement by a White House spokesperson, it claimed the operation was undertaken to ‘defend Saudi Arabia's border and to protect Yemen's legitimate government … at the request of Yemeni President … Hadi’.Footnote 40 Other States also expressed their support for the intervention. For example, the United Kingdom emphasized its ‘firm political support for the Saudi action in Yemen, noting that it was right to do everything possible to deter Houthi aggression’.Footnote 41 Similarly, France ‘reaffirm[ed] its support for Yemen's government and for President Hadi’, adding that the country ‘stands alongside its partners in the region in their efforts to restore Yemen's stability and unity’.Footnote 42 Finally, the Canadian Minister of Foreign Affairs stressed that ‘Canada supports the military action by Saudi Arabia and its Gulf Cooperation Council (GCC) partners and others to defend Saudi Arabia's border and to protect Yemen's recognized government at the request of the Yemeni president’.Footnote 43
At the same time, some States and organizations adopted a more cautious approach. EU High Representative for Foreign Affairs Federica Mogherini, declared ‘that military action is not a solution’, while noting that the ‘Yemeni civilian population, already affected by dire living conditions, are the first victims of the current military escalation’.Footnote 44 This was in line with the reaction of UN Secretary-General Ban Ki-moon, who pointedly recalled the Security Council's presidential statement of 22 March, which, ‘while supporting the legitimacy of the President of Yemen, … called on all Member States to refrain from external interference which seeks to foment conflict and instability and instead to support the political transition’.Footnote 45
Outspoken criticism regarding the legality of the operation was nonetheless noticeably absent, barring few exceptions. Unsurprisingly, the strongest reaction came from Iran, which condemned the air raid on Yemen, saying it ‘goes on in flagrant defiance of the most basic principles of international law, flouting the purposes and principles of the Charter of the United Nations, in particular the obligation to refrain from the threat or use of force in international relations’.Footnote 46 Ayatollah Khamenei called the intervention ‘a genocide that can be prosecuted in [international] courts’.Footnote 47 Russia issued a comment calling on all parties and their external allies to ‘immediately cease any forms of warfare and give up attempts to achieve [their] goals through military force’.Footnote 48 Later in April, Foreign Minister Lavrov further claimed that ‘as of now [the Saudi-led operation] has no international legal foundation’.Footnote 49 Finally, the Iraqi president also stated that there was ‘no logic to the operation at all’ and that ‘the problem of Yemen is within Yemen’.Footnote 50 These comments were in line with a previous statement of the Foreign Minister, stating that ‘bringing external forces is not right’ as it was the position of Iraq to ‘resort to legitimacy and non-interference in Yemen's internal affairs’.Footnote 51
The Operation itself was only addressed at the level of the UN Security Council on 14 April 2015, ie, almost three weeks after it was launched.Footnote 52 Resolution 2216(2015),Footnote 53 adopted at the start of the session, ‘reaffirms’ the Council's ‘support for the legitimacy of the President of Yemen, Abdo Rabbo Mansour Hadi’, while ‘condemning in the strongest terms the ongoing unilateral actions taken by the Houthis’. Although the resolution does not go as far as to provide ex post facto authorization for Operation Decisive Storm, it does not contain any explicit or implicit criticism of the operation. Instead, the preamble takes note of the request of Yemen for military support addressed to the GCC as well as of the letter of the five Gulf States to the Security Council dated 26 March. The operative part of the resolution focuses exclusively on the Houthi rebels, providing for an expansion of the arms embargo and travel ban on rebel leaders.Footnote 54 The Houthi rebels are further ‘demanded’ inter alia to immediately end the use of violence; to ‘cease all actions that are exclusively within the authority of the legitimate Government of Yemen’, and to ‘refrain from any provocation or threats to neighbouring States, including through acquiring surface-surface missiles, and stockpiling weapons in any bordering territory of a neighbouring State’.
In the ensuing debate, numerous Council Members expressed support for President Hadi as the legitimate representative of the Republic of Yemen,Footnote 55 while denouncing the Houthi rebels as the ‘spoilers’ of Yemen's political transition.Footnote 56 Although the legal basis of Operation Decisive Storm was not directly addressed,Footnote 57 the United Kingdom in general terms expressed ‘support [for] the Saudi-led military intervention in Yemen taking place at the request of President Hadi’.Footnote 58 Chad for its part ‘support[ed] the efforts of the member countries of the [GCC] to restore peace in Yemen’.Footnote 59 On the other hand, several members emphasized that military action could not possibly solve the crisis in Yemen.Footnote 60 In addition, some States expressed disappointment over the one-sided nature of the Council resolution. Notably, the Russian Federation explained that it had abstained during the vote, given that ‘the sponsors [of the resolution] refused to include the requirements … , which were addressed to all parties to the conflict, to swiftly halt fire and begin peace talks’.Footnote 61 This concern was echoed by Venezuela, which had ‘hoped that today's resolution would include stronger language on a cessation of hostilities—and indeed every kind of military action—in Yemen’.Footnote 62 Still, no single Council member (not even Russia) explicitly questioned the legality of Operation Decisive Storm.
Having regard to the fierce debates that similar interventions have given rise to in the past, the complete lack of an in-depth debate and legal analysis regarding Operation Decisive Storm is flabbergasting. Besides the handful of unequivocal statements by state officials which have been cited, and a few (brief) legal opinions circulating the blogosphere,Footnote 63 the silence on the legality of the operation is indeed deafening.
IV. CLAIMING SELF-DEFENCE AGAINST THE HOUTHI ‘AGGRESSION’
The obvious starting point for a legal evaluation of Operation Decisive Storm is the justification offered by Saudi Arabia and its main allies in their letter to the Security Council of 26 March 2015.Footnote 64
As mentioned before, the letter puts forward a variety of arguments. First, it refers to a request from President Hadi for ‘support … to protect Yemen and its people from the aggression of Houthi militias’, and ‘help in confronting terrorist organizations’.Footnote 65 Second, the foreign-instigated aggression by the Houthi ‘puppets’Footnote 66 against Yemen is perceived as constituting a threat to regional and international peace and security. Third, the presence of heavy weapons beyond the control of legitimate authorities, the build-up of military presence in the border-region, and the former attack against Saudi Arabian territory (in 2009), taken together, allegedly qualify as a grave threat to the region in general, and Saudi Arabia in particular.Footnote 67 However, in the statements by Hadi and by the Arab League, the alleged foreign-backed ‘aggression’ emerges as the main justification for the intervention. In the light of this, this section will first consider the possible right to (collective and individual) self-defence, before proceeding to a discussion of the ‘intervention by invitation’ doctrine based on president Hadi's request.Footnote 68
A. The Right to Collective Self-Defence
In his letter to the GCC, president Hadi invoked the collective self-defence provisions enshrined in Article 51 UN Charter, in the Arab League Charter and the Arab Treaty of Joint Defense (the same provisions were also cited by the Arab League). He urged the six countries ‘to provide immediate support … and take the necessary measures, including military intervention, to protect Yemen and its people from the ongoing Houthi aggression’.Footnote 69 Five out of six GCC member States, excluding the Sultanate of Oman, concurred with his qualification of the Yemeni crisis as an aggression by Houthi militiasFootnote 70 and ‘decided to respond to President Hadi's appeal’, by launching Operation Decisive Storm.
It is clear that for the Operation to qualify as a proper exercise of the right of collective self-defence, multiple requirements must cumulatively be fulfilled. As indicated in the Nicaragua case, reliance on the right to collective self-defence requires that a State declares itself to be the victim of an armed attack and specifically calls for military support.Footnote 71 In addition, the ordinary requirements for individual self-defence must of course be fulfilled on the part of the State requesting military assistance.
In the present case, the formal requirements would prima facie seem to be met. In particular, Hadi expressly declared that his country was the victim of ‘aggression’ and specifically requested military assistance from the GCC countries. In a similar vein, as is implicitly acknowledged in Security Council resolution 2216(2015), the requirement that measures in self-defence be reported to the Council was complied with. At the same time, a crucial reservation is necessary. By analogy with ‘consent’ as a ground for precluding wrongfulness under the law of international responsibility, and in the context of the ‘intervention by invitation’ doctrine, reliance on a request for military assistance by a victim State presupposes that this request emanates from a person that is competent to express the will of the State in such a matter. Given that President Hadi and his government were engaged in a non-international armed conflict with the Houthi rebels and lacked effective control over significant parts of the territory at the moment the letter was sent, it can be questioned whether they still had that authority. Since the substantive analysis in this context is identical to the evaluation of the validity of State consent in the context of the ‘intervention by invitation’ doctrine, these concerns will be addressed in greater depth in the section below.Footnote 72
In any event, reliance on collective self-defence only provides a viable legal basis if it is shown that Yemen effectively fell victim to an ‘armed attack’ in the sense of Article 51 UN Charter. Evidently, this concept does not extend to forcible acts that are of a purely ‘intra-State’ nature, but presupposes some external component. The external aspect will be clear where an armed attack emanates directly from a third State. Alternatively, it may stem from a third-State's high degree of involvement in attacks carried out by a non-State armed group (NSAG). This is the ‘indirect military aggression’ scenario envisaged in Article 3(g) of the UNGA Definition of Aggression.Footnote 73 Finally, inasmuch as it is accepted that attacks by non-State entities can ipso facto, irrespective of any form of State involvement, qualify as ‘armed attacks’—which admittedly remains controversial—the external aspect can consist in the cross-border nature of the attacks themselves (eg where attacks are launched or directed from abroad).Footnote 74
Of these three scenarios, the first is patently inapplicable in the present context. Similarly, the third scenario can easily be discarded without there being need for revisiting in detail the lingering controversy over the right of self-defence against non-State actors.Footnote 75 Indeed, the rebels (consisting primarily of Houthi fighters and former president Saleh loyalists) were undeniably Yemeni citizens and their armed insurrection was clearly of a domestic nature.Footnote 76 This is also acknowledged by the Hadi-led government, which declared that the Houthi attacks targeted ‘the country's sovereignty’ and aimed at ‘dismembering Yemen and undermining its security and stability’. The Houthi attacks were not of a cross-border nature—nor did the Houthi rebels have a settled (armed) presence abroad. In sum, leaving aside for a moment the alleged Iranian involvement (see below), the rebellion as such was thus waged by Yemenis against Yemenis, and cannot be regarded as an external armed attack.
It may be objected that the Hadi statement and the letter of the five Gulf States also made reference to the role of terrorist organizations operating in Yemen, such as Al-Qaida and ISIS.Footnote 77 Even if, in contrast to the Houthi rebels, these groups may have been operating on a cross-border basis, the threat posed by them figures only as a subsidiary concern in the justifications put forward in defence of Operation Decisive Storm. In any case, again leaving aside the controversy regarding self-defence against non-State attacks, and leaving aside whether possible cross-border attacks by these terrorist groups were sufficiently grave to qualify as ‘armed attacks’, this could at most justify forcible action against terrorist strongholds. By contrast the threat posed by these terrorist groups could not justify a military operation that primarily targeted the Houthi rebels.
This leaves only the ‘indirect military aggression’ scenario as a viable option. It is clear from the statements above that President Hadi and the intervening countries claimed the Houthi rebellion to be backed by ‘regional Powers’.Footnote 78 Somewhat surprisingly, the Hadi statement and the letter of the Gulf countries to the Security Council do not expressly identify the third State(s) allegedly orchestrating the Houthi coup, let alone provide indications on the type and degree of support to the Houthis.Footnote 79 Still, it is clear from comments by high-profile Yemeni officials,Footnote 80 and from the continued labelling of the Yemeni crisis as a ‘proxy war’,Footnote 81 that references to a ‘foreign’, ‘regional’, or ‘outside’ force allegedly behind the Houthi uprising alluded to the involvement of the Islamic Republic of Iran.
As mentioned above, ‘indirect military aggression’ of this type is envisaged in Article 3(g) of the UNGA Definition of Aggression. In the Nicaragua case, the International Court of Justice (ICJ) famously used this provision as the basis to determine the permissibility of self-defence in a proxy warfare context:
An armed attack must be understood as including not merely action by regular armed forces across an international border, but also ‘the sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to’ (inter alia) an actual armed attack conducted by regular forces, ‘or its substantial involvement therein’. This description, contained in Article 3, paragraph (g), of the Definition of Aggression … , may be taken to reflect customary international law. … the Court does not believe that the concept of ‘armed attack’ includes … assistance to rebels in the form of the provision of weapons or logistical or other support. Such assistance may be regarded as a threat or use of force, or amount to intervention in the internal or external affairs of other States.Footnote 82
It follows from this dictum that an armed attack takes place where a third State ‘sends’ armed bands or irregulars who carry out attacks. Given that there is no evidence whatsoever that Iran actually ‘sent’ armed bands or groups across borders to instigate a civil war in Yemen, this scenario can be discarded for present purposes. The ICJ nonetheless seems to envision an alternative scenario whereby a third State is ‘substantially involved’ in the acts of armed bands or irregulars carrying out attacks.Footnote 83 However, it is not entirely clear what this ‘substantial involvement’ criterion actually entails. The ICJ ostensibly adopted a restrictive reading by excluding the ‘provision of weapons or logistical or other support’.Footnote 84 This narrow approach was, however, strongly criticized by Judges Jennings and Schwebel.Footnote 85 It has also increasingly come under strain in post-Cold War practice.Footnote 86
It has been argued that foreign support must be essential in the armed group's ability to commit (what could be qualified as) an armed attack, for the right to self-defence to be triggered.Footnote 87 Reference in this regard is sometimes made to the ‘overall control’ test, as pronounced by the International Criminal Tribunal for the Former Yugoslavia's (ICTY) Appeals Chamber in its seminal Tadić judgement.Footnote 88 That test encompasses the ‘organising, coordinating or planning the military actions of the military group, in addition to financing, training and equipping or providing operational support to that group’.Footnote 89 Admittedly, the ICJ in the Bosnian Genocide case disavowed this test, but solely for the purpose of establishing the attributability of acts committed by paramilitary units to the State. By contrast, it acknowledged that ‘[i]nsofar as the “overall control” test is employed to determine whether or not an armed conflict is international … it may well be that the test is applicable and suitable’.Footnote 90 If one were to follow this line of thought, possible ‘overall control’ by Iran over the Houthi movement might not only ‘internationalize’ the conflict, but also provide the necessary ‘external’ component for purposes of identifying an ‘armed attack’ against the State of Yemen in the sense of Article 51 UN Charter. Yet, whether this threshold of control over, or support to, the rebel actions was met in the case under examination seems highly questionable.
On the one hand, some evidence seems to support the allegations of ties between Iran and the Houthi movement. For example, on 23 January 2013 the Yemeni authorities apprehended an arms vessel, allegedly bound for the Houthis, carrying Iranian weapons, including explosives, rocket-propelled grenades and ammunition.Footnote 91 Similarly, the Houthis signed an agreement with Iran following the takeover of Sana'a to allow for 14 flights per week between the two countries. It was alleged to serve as a supply route to the rebels.Footnote 92 Furthermore, there are indications that Islamic Revolutionary Guard Corps personnel have trained the Houthis.Footnote 93 Finally, the UN Panel of Experts on Yemen observes that the release of Iranian prisoners immediately after the Houthis took control of Sana'a indicates ‘the depth of the relationship’.Footnote 94
On the other hand, the intervening States remained remarkably vague about the nature and extent of the Iranian involvement and did not put forward any evidence to corroborate their allegations. In the Security Council debate of 14 April, none of the Council members even mentioned Iran by name. Moreover, the involvement by Iran in the Houthi armed campaign against the Yemeni government was trivialized, or even flatly denied, by the two protagonists themselves.Footnote 95 Some commentators opined that ‘Saudi Arabia [was] grossly exaggerating Iran's power in Yemen to justify its own expansionist ambitions’,Footnote 96 or expressed concern that ‘few of the claims [regarding Iranian involvement] [were] based on independent evidence’.Footnote 97
Two statements by Saudi and US officials concerning Iranian–Houthi ties are particularly revealing with the tentative threshold in mind. First, when asked about Iranian involvement in the conflict, the (then) Saudi ambassador to the United States merely referred to ‘reports that the Iranians are providing weapons and training and advisors to the Houthis’.Footnote 98 Second, a spokesperson for the US Department of State was even more explicit by stating as follows: ‘we are aware of reports of a variety of support provided by Iran to the Houthis, but we have not seen evidence that Iran is exerting command and control over the Houthis activities in Yemen’.Footnote 99 It follows that even the principal interventionist States did not go as far as to claim that Iran has a role in organizing, coordinating or planning the military actions of the Houthis, in addition to purely material and operational support. In light of the foregoing, the requirement of an (external) ‘armed attack’ does not seem met. The right to collective self-defence can therefore arguably be ruled out as a potential legal justification for Operation Decisive Storm.
B. Right to Individual Self-Defence
Another element that is prominent in the discourse of the intervening States is the existence of an allegedly serious threat to Saudi Arabian security and territorial integrity. Thus, the statement of the five Gulf countries of 26 March reads as follows:
[The Houthi militias] have continued … to build up a military presence, including heavy weapons and missiles, on the border of Saudi Arabia. They have recently carried out large-scale military exercises using medium and heavy weapons, with live ammunition, near the Saudi Arabian border. The Houthi militias have already carried out a bare-faced and unjustified attack on the territory of Saudi Arabia, in November 2009, and their current actions make it clear that they intend to do so again.Footnote 100
The US approval of the operation similarly referred to the need to ‘defend Saudi Arabia's border’.Footnote 101 This raises the question whether Operation Decisive Storm could be framed as an exercise of the right of individual self-defence on the part of Saudi Arabia.Footnote 102 This hypothesis inevitably poses questions (again) regarding the permissibility of self-defence against attacks by non-State actors (a matter we will not revisit here), but also regarding the application ratione temporis of the latter right.
At the outset, it hardly requires explaining that the ‘barefaced and unjustified’ attack by Houthi fighters against Saudi Arabia of November 2009 alluded to—whatever the gravity and exact circumstancesFootnote 103—cannot justify action in self-defence six years later. Such an approach would run foul of the necessity criterion, which is inherent to the right of self-defenceFootnote 104 (and in particular the ‘immediacy’ requirement implicit in that criterion), which prescribes a response within ‘an appropriate time frame, a period which preserves the credibility of the primary character of [a defensive act] as being repelling’.Footnote 105 To hold that past transgressions can justify the reactivation of the right of self-defence in the absence of a new casus foederis—would make a mockery of the jus contra bellum.
Having established that there was no prior ‘armed attack’, could Saudi Arabia nonetheless invoke the right of self-defence in light of the threat posed by the Houthi rebels? Since the 9/11 attacks, and the promulgation of the ‘Bush doctrine’,Footnote 106 scholars and States have increasingly embraced the view that Article 51 UN Charter allows for anticipatory self-defence against ‘imminent’ threats of attack.Footnote 107 This view is generally construed along the lines of the so-called Caroline formula, which speaks of ‘a necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation’.Footnote 108 While this view remains controversial and finds little support in State practice,Footnote 109 it is beyond doubt that the permissibility of self-defence against more remote, ‘non-imminent’ threats of armed attack has been widely denounced throughout the international community after 9/11Footnote 110—a position implicitly subscribed to by the ICJ in the Armed Activities case.Footnote 111
In the present case, however, no evidence has been offered to suggest that the Houthis were planning an armed attack on Saudi soil, let alone that it had entered the implementation phase—no proof was furnished of an identifiable ‘imminent’ armed attack.Footnote 112 The GCC statement merely presents indications of a potentially hostile attitude: (1) the Houthi military presence and exercises near the Saudi Arabian border, and (2) the experience of the 2009 armed conflict pitting Houthi militias against Yemeni and Saudi armed forces.Footnote 113 This then allegedly implies the intent to launch another ‘unjustified attack on the territory of Saudi Arabia’.Footnote 114
Regarding the former element, a senior Gulf Arab official reportedly stated that ‘the US government had confirmed that … some of Yemen's estimated 300 Scud missiles, under rebel control, had been moved close to the Saudi border’.Footnote 115 It may also be recalled that Security Council resolution 2216(2015) appears to acknowledge the threatening posture of the Houthi rebels inasmuch as the latter are demanded to ‘refrain from any provocation or threats to neighbouring States, including through acquiring surface-surface missiles, and stockpiling weapons in any bordering territory of a neighbouring State’. However, the Houthi base of operations was the northern governorate of Sa'ada, which borders on Saudi Arabia.Footnote 116 The build-up of military equipment there, reportedly even tested during military exercises, was therefore not surprising, given the protracted armed conflict going on between Houthi and government forces and Saudi Arabia's anti-Houthi stance in the 2009 conflict. It does not provide strong evidence for an intent to launch a cross-border attack, but might well have been intended as a defensive measure against a possible Saudi intervention.
In conclusion, Operation Decisive Storm cannot be legally justified by reference to Saudi Arabia's right of individual self-defence. The 2009 conflict between Saudi Arabia and the Houthis had clearly gone beyond its expiration date to serve as a trigger for recourse to self-defence. In addition, no convincing evidence was put forward to prove an imminent armed attack against Saudi Arabia. The Houthi threat might well have justified preparatory measures on the part of Saudi Arabia, enabling that country to ‘be ready in case an attack came’ (to paraphrase the words of US Governor Stassen),Footnote 117 but could not justify anticipatory action in self-defence.
V. A VALID REQUEST FOR MILITARY ASSISTANCE BY PRESIDENT HADI?
A. Introduction
After disproving claims that self-defence might provide an adequate legal justification for Operation Decisive Storm, a final interpretation of the March statement centres on the appeal by president Hadi to ‘come to the country's aid’ and ‘provide immediate support in every form and take the necessary measures, including military intervention, to protect Yemen and its people from the ongoing Houthi aggression’.Footnote 118
Article 2(4) of the UN Charter prohibits any and all use of transboundary armed force.Footnote 119 However, if a State requests that force be used by allied States upon its territory, or consents thereto, such force hardly goes against that State's ‘territorial integrity or political independence’, much less affects ‘the international relations’ between the States concerned.Footnote 120 Since each State ‘enjoys the rights inherent in full sovereignty’,Footnote 121 it is also free to dispose of its territory, including by allowing military operations by other States within its national borders.Footnote 122 In such case, the argument goes, no breach of the primary rule prohibiting recourse to force materializes.Footnote 123
This general rule, whereby States can request foreign military assistance without violating Article 2(4) of the UN Charter, is commonly referred to as the ‘intervention by invitation’ doctrine.Footnote 124 The legality of such intervention follows a contrario from Article 3(e) of the UN General Assembly Definition of Aggression.Footnote 125 It finds support in the practice of the UN Security CouncilFootnote 126 and is broadly acknowledged in legal doctrine.Footnote 127 Furthermore, the ICJ has lent credence to the rule in the Nicaragua case, where the Court emphasized:
[I]t is difficult to see what would remain of the principle of non-intervention in international law if intervention, which is already allowable at the request of the government of a State, were also to be allowed at the request of the opposition.Footnote 128
The Court again confirmed its pronouncement (a contrario) in the Armed Activities case.Footnote 129
Consequently, there exists a presumption that a use of force on foreign territory with the host State's consent generally does not violate international law. Against this background, it is rather surprising that the main protagonists chose to frame Operation Decisive Storm primarily by reference to the right of self-defence, instead of the ‘intervention by invitation’ doctrine, which would, on first sight, seem to provide a more plausible legal justification. This is not to say that reliance on the latter legal basis does not pose any challenges. Indeed, reliance on intervention by invitation is of course preconditioned on the validity of the request, and is sometimes claimed to be excluded in situations of civil war. These are the two issues that most cast a shadow over the permissibility of the Saudi-led intervention in Yemen, and, conversely, where the precedential effect of the intervention may most make itself felt. It is to these two issues that we now turn.
B. Validity of State Consent
The ‘legalizing effect’ of State consent, described above, is dependent upon its intrinsic validity.Footnote 130 According to general international law, four conditions need to be fulfilled. First, in light of the impact on the State's territorial integrity or inviolability, consent for the act must emanate from the highest authorities of the State.Footnote 131 Second, the State's agreement must not be vitiated, and, in particular, should not be produced through the coercion of a representative of the State.Footnote 132 Third, the consent must have been given prior to the intervention.Footnote 133 This follows from the principle that ex post facto consent cannot serve to expunge the prior breach of the prohibition on the use of force.Footnote 134 Finally, and logically, the foreign military assistance needs to remain within the scope of the consent.Footnote 135
More fundamentally, especially for the purposes of this article, it is solely ‘within the sovereign prerogative of a State and its government to give … consent in the form of a request’.Footnote 136 While Gray (euphemistically) observes that ‘State practice has not produced uniform doctrine as to who counts as the government with the right to outside intervention’,Footnote 137 it is generally presumed that the bearer of this sovereign prerogative needs to meet two, interrelated requirements: (1) exercise effective control over the State's territory and (2) enjoy international recognition.Footnote 138 Regarding the first element, State practice supports the view that intervention by invitation is excluded in a situation of State failure or anarchy.Footnote 139 At the same time, it is argued that a minimum of effectiveness can be sufficient.Footnote 140 According to Nolte, for instance, this condition is met where the authorities retain ‘control over a sufficiently representative part of the State territory’, thereby excluding ‘phony governments, puppet regimes, [and] governments in exile’.Footnote 141 The second element relates to the consenting entity enjoying widespread international recognition, in relation to which the position taken by the United Nations, and regional organizations, has significant probative value.Footnote 142
According to the traditional view, States are required to ‘accord recognition in fulfilment of the duty not to withhold the benefits of international personality from a State represented by a government whose rule is accepted by the population’.Footnote 143 In other words, the faction exercising effective control over the territory, approved by a ‘substantial expression of national will’,Footnote 144 is entitled to international recognition by other States. However, in a situation of grave internal turmoil between a rebel faction and the de jure regime, resulting in the latter's loss of effective control over a large part of the territory, international law maintains a presumption in favour of the established government:
[s]o long as the lawful government, however adversely affected by the fortunes of the civil war, remains within national territory and asserts its authority, it is presumed to represent the State as a whole. … In one respect, however, the presumption in favour of the lawful government is above controversy: the latter is entitled to continued recognition de jure so long as the civil war, whatever its prospects, is in progress.Footnote 145
Some commentators seem to add a third criterion, ie, democratic legitimacy.Footnote 146 It has been argued that ‘effectiveness’ and ‘(democratic) legitimacy’ operate to some extent as communicating vessels and that ‘the legitimacy of origin of a government can sometimes offset its lack of effectiveness’.Footnote 147 By contrast, democratic legitimacy alone, would not seem sufficient of itself for the purpose of inviting foreign troops absent a minimum degree of effectiveness. Based on an analysis of State practice, Corten finds that a democratically elected leader that is ousted from power by domestic forces and who no longer holds effective control over territory, is not in a position to validly request military assistance.Footnote 148 In such settings (eg, in the case of the overthrow of the Haitian President Aristide in the early 1990s),Footnote 149 States and regional organizations have not claimed a right of ‘pro-democratic’ intervention by invitation, but have rather sought the formal backing of the UN Security Council.Footnote 150
The Russian intervention in Crimea early 2014 offers a good illustration of how the doctrine, as described above, is applied in practice. Russia indeed justified the deployment of troops on the Crimean peninsula by referring, inter alia, to a prior and written request by President Yanukovych.Footnote 151 The reactions within and without the UN Security Council nonetheless reveal that Yanukovych, who had effectively been removed from power by a large majority of the Ukrainian Rada (albeit in a manner formally incompatible with the Ukrainian Constitution) and fled the country, was no longer regarded competent to express the will of the Ukrainian State.Footnote 152 The British representative to the United Nations phrased it as follows:
The Russian representative claims that Mr. Yanukovych has called for Russian military intervention. We are talking about a former leader who abandoned his office, his capital and his country; whose corrupt governance brought his country to the brink of economic ruin; who suppressed protests against his Government leading to over 80 deaths; and whose own party has abandoned him. The idea that his pronouncements now convey any legitimacy whatsoever is far-fetched and in keeping with the rest of Russia's bogus justification for its actions.Footnote 153
In other words, the ousted Ukrainian president had clearly lost all effective control over the territory.Footnote 154 This is further evidenced by the fact that he was already in exile at the moment of his request.Footnote 155 Moreover, he was no longer recognized by the international community as the legitimate representative of the Ukrainian government.Footnote 156 Consequently, he did not have the authority to consent to foreign military intervention.
Against this background, how does Operation Decisive Storm fare? Undoubtedly, the Hadi government had lost much effective control over Yemen by the time it issued a request for foreign military assistance. Houthi forces had taken control over the capital Sana'a since September 2014 and effectively ran the central government ever since. President Hadi and other members of his government had also been put under house arrest and submitted their resignation (only to rescind it after fleeing to Aden).Footnote 157 However, in March 2015, President Hadi still asserted control over parts of Yemen, particularly in the south and east of the country.Footnote 158 He enjoyed the support of sections of the armed forces, several governorate and tribal authorities, and the so-called popular resistance committees.Footnote 159 As a consequence, some denied the Houthi's capacity to take control over the entire country.Footnote 160
How then does the reaction by the international community with regard to the Russian intervention in Crimea compare with Operation Decisive Storm? In both cases, a democratically elected leader was driven from power, sought refuge in a neighbouring country and called for outside military support. Yet, whereas the Russian intervention was expressly denounced as unlawful by numerous States, the Saudi-led operation was approved by the League of Arab States as well as by several other States, without any Security Council member explicitly challenging its legality. Security Council resolution 2216 (2015) even ‘took note’ of Hadi's request for outside support, implicitly lending credence to its validity. Russian news agencies were quick to note the parallels between the two operations. Conversely, when quizzed about the possible parallels, US State Department Spokesperson Marie Harf remained strikingly vague.Footnote 161
Sceptics may be inclined to conclude that the difference in reaction is purely arbitrary, and that the intervention by invitation doctrine does not lend itself to objective external assessment, but simply bends whichever way the political wind blows. Yet it is necessary to ascertain if there are certain distinguishing features which allow the intervention by invitation doctrine to be confirmed, or refined rather than denied or discarded. In casu, the key distinguishing feature appears to be that, in spite of the significant loss of effective control, Hadi remained the undisputed legitimate president of Yemen in the eyes of the international community. On several occasions, the UN Security Council demanded that all attacks against ‘the legitimate authorities’ must ceaseFootnote 162 and reaffirmed its ‘support for the legitimacy of the President of Yemen’, even after his government's flight to Riyadh.Footnote 163 In a similar vein, the ‘legitimacy’ of President Hadi was stressed by numerous Council members in the Security Council debate of 14 April 2015Footnote 164 and in other statements by individual States.Footnote 165 Undoubtedly, such endorsement of Hadi's legitimacy by the Security Council, and by the international community more generally,—which stands in marked contrast to the lack of international support for former President Yanukovych—carries significant weight. Moreover, President Hadi and his government seemed to still command at least some obedience in the south and east of the country at the time of the request, which was issued days prior to their flight to Riyadh.
The tentative lesson to be drawn from this is, first, that the broad international recognition of the person inviting outside intervention may effectively compensate to a large extent for the lack of effective control over territory, thereby seemingly corroborating the aforementioned presumption in favour of the established de jure regime as expressed by Lauterpacht.Footnote 166 What is more, the Saudi-led intervention in Yemen may well be invoked in future cases as a precedent by States seeking to respond to a request for military intervention by a leader that is, for instance, on the verge of being ousted by a military coup, and in particular when that leader still enjoys broad international support. The reverse side of the coin is that intervening States may be less inclined to have the intervention sanctioned by the UN Security Council—especially when a permanent member is ill-disposed towards it.
In the end, Gray notes that
in Security Council and General Assembly debates on the use of force, although there has been discussion of the reality of the invitation and of the effectiveness or legitimacy of the government concerned, the main focus has been on the substantial issue of whether the invitation was a mere pretext for intervention.Footnote 167
It is here that an additional difficulty arises. Indeed, one cannot ignore that Operation Decisive Storm did not constitute a response to a coup d’état by a military clique, but was launched against the background of a full-scale armed conflict between rival factions. As is explained below, however, the permissibility of intervention by invitation in such a context is anything but a given.
C. Presumption That Intervention by Invitation Is Excluded in Case of a Civil War
Even if it were accepted that the widespread international recognition on the part of Hadi meant that he could, in principle, validly invite outside military support, one cannot ignore that the permissibility of ‘intervention by invitation’ in a civil war context has long been highly controversial.
Scholars are divided on this issue in two main schools of thought.Footnote 168 The first endorses the so-called ‘negative equality’ doctrine,Footnote 169 or ‘strict abstentionism’.Footnote 170 It subscribes to the view expressed in the Wiesbaden resolution, adopted in 1975 by the Institut de Droit International, which stipulates that ‘[t]hird States shall refrain from giving assistance to parties in a civil war which is being fought in the territory of another State’.Footnote 171 It thus proclaims that as soon as the threshold for a civil war is reached, consent by the government for the use of force on its territory ceases to perform its legalizing effect.Footnote 172 This view—also subscribed to in a UK Foreign Policy Document of 1984Footnote 173—is premised on the idea that no warring faction can represent the State during an internal armed conflict.Footnote 174 It is supported by reference to the principle of non-intervention,Footnote 175 read in conjunction with the right of self-determination. The former inter alia prohibits ‘interference in civil strife in another State’, or ‘assisting or participating in acts of civil strife’.Footnote 176 The right to self-determination moreover prescribes that ‘all peoples have the right freely to determine, without external interference, their political status … ’.Footnote 177 It is submitted that situations where opposing factions have taken up arms to determine a country's political fate, fall within its scope. Moreover, the bearers of this right are ‘peoples’, a term which is generally accepted to mean ‘the constituent people of a certain territorial entity formed by history’.Footnote 178 In cases of civil war without an element of colonial domination, alien occupation, or racist oppression,Footnote 179 ‘people’ can therefore refer to the entire population of the territorial State.Footnote 180 In all, the underlying rationale is that outside intervention for the benefit of one of the warring parties in a civil war would thus interfere with the people's right to decide their own future.Footnote 181 Moreover, given that respect for self-determination is one of the purposes of the United Nations, such an intervention would violate Article 2(4) of the UN Charter.Footnote 182
The second school of thought firmly opposes such a reading of international law. It opts for the ‘government preference’ approach, which draws a prima facie dichotomy between foreign military aid to the government (allowed) versus rebel forces (prohibited). Scholars supporting this approach note that it best corresponds to ‘traditional international law’.Footnote 183 More fundamentally, it is argued that modern State practice flatly contradicts the idea that providing military assistance to a government is excluded in cases of a civil war.Footnote 184 Reference in this regard has been made to recent interventions in Mali (2013) and Iraq (2014).Footnote 185
In the end, while the Nicaragua case does not cut the Gordian knot, proponents of the first school of thought (traditionally the majority view in the Charter era) (still) seem to have the upper hand. Indeed, the combined effect of the non-intervention principle and the right of self-determination ostensibly serves to exclude military intervention by invitation in civil war.Footnote 186 While an in-depth review is beyond the scope of the present article, State practice generally corroborates this approach, in that States have never asserted a (general) right to intervene militarily on the side of a de jure government engaged in a non-international armed conflict, but have rather sought to defend their conduct by relying upon exceptions to a general prohibition of such interference in civil strife (chiefly counter-intervention; see below).Footnote 187 To paraphrase the ICJ, the rule is therefore actually confirmed, rather than weakened.Footnote 188 It follows that there arguably exists a presumption against intervention by invitation in civil wars.
In this context, it must be emphasized that, whatever the precise threshold one applies,Footnote 189 the conflict in Yemen—at a time when the Houthi rebels were in possession of large parts of the national territory—undoubtedly qualified as one. Still, State practice and legal doctrine suggest that the presumption against intervention by invitation in civil war scenarios may be rebutted when the intervention does not imply actual interference in the civil strife and/or does not adversely affect the right of self-determination.Footnote 190
D. Rebutting the Presumption against Intervention by Invitation in Civil War Scenarios
1. Intervention supporting the fight against terrorism
It is easy to conceive of scenarios where an intervention by invitation takes place ‘against the background of’ a civil war, but does not interfere therewith and does not adversely affect peoples' right to self-determination. Examples include third-State action, with prior State consent, limited to rescuing nationals abroad, carrying out limited police or ‘hot pursuit’ operations, or supporting peacekeeping missions.Footnote 191 More controversially, it has been argued that the right to self-determination does not impede a State from requesting outside military assistance in fighting terrorist armed groups operating on its territory.Footnote 192 Such third-State support would not be directed at forcefully deciding the outcome of a purely internal fight, but rather at combatting ‘one of the most serious threats to international peace and security’.Footnote 193
Recent instances of State practice, such as the French intervention in Mali in 2013 (Opération Serval),Footnote 194 or the air strikes by a US-led coalition of the willing against ‘Islamic State’ in Iraq,Footnote 195 both of which were requested by the de jure authorities and both of which were generally welcomed, support this view. The former operation was carried out in early 2013 ‘by the French forces, at the request of the transitional authorities of Mali’ aimed exclusively at stopping ‘the offensive of terrorist, extremist and armed groups towards the south of Mali’Footnote 196—France indeed insisted that it was not intervening in the conflict between the government in Bamako and the Tuareg rebels of the MLNA, but was only acting against Islamist terrorist groups partly composed of foreign elements.Footnote 197 A legal analysis in the context of, inter alia, ‘intervention by invitation’ has already been conducted elsewhere.Footnote 198 Suffice it to emphasize that France ‘responded … to a request for assistance from the Interim President of the Republic of Mali’ for the purpose of ‘supporting Malian units in combating those terrorist elements’.Footnote 199 Additionally, the intervention was ‘welcomed’ by the United NationsFootnote 200 and supported by a significant part of Malian popular opinion.Footnote 201 In other words, the intervention did not effectively (try to) arbitrate a purely internal political strife.
The second example is the American-led multinational intervention in Iraq to combat Islamic State, following its establishment of an Islamic caliphate by the end of June 2014 in a territory covering parts of Syria and Iraq.Footnote 202 No discussion arose over the legality of the military operations within Iraqi territory,Footnote 203 which was launched pursuant to a request by the Iraqi authorities for ‘the United States of America to lead international efforts to strike ISIL sites and military strongholds’.Footnote 204 The absence of legal objections may well be inspired by the acceptance, widely shared within the international community, that, rather than qualifying as a domestic insurgent movement,Footnote 205 Islamic State undoubtedly constituted a terrorist organizationFootnote 206 (which moreover operated on a cross-border basis).Footnote 207
Accepting that governments engaged in a non-international armed conflict may request military assistance to fight ‘terrorist’ groups gives rise to the distinct problem of distinguishing between such ‘terrorist groups’ and other (more legitimate) non-State armed groups. This is of course a highly politicized issue. Future evolutions in State practice will have to clarify if the exception stands and how it applies. In any case, in Yemen, the coalition's efforts were without a doubt primarily aimed at repelling the ‘internal’ Houthi ‘militias’,Footnote 208 as evidenced by its choice of targets on Yemeni soil. By contrast, the fight against recognized terrorist groups such as Al-Qaida and Islamic State was not at the forefront of the military operations. Consequently, the intervening States undoubtedly took sides in the civil strife going on within Yemeni territory, thus putting the intervention at odds with fundamental norms of international law.
If Operation Decisive Storm clearly interfered with the civil strife on Yemeni territory, could one nonetheless argue that it did not undermine the Yemeni people's right to self-determination? This hypothesis is further explored below.
2. Counter-intervention and intervention to promote the right of self-determination?
State practice reveals that, save for rare exceptions, States intervening in civil wars have almost invariably argued that they did so in response to prior outside intervention against the government, ie, as a form of ‘counter-intervention’.Footnote 209 Interestingly, the cited 1984 UK Foreign Policy Document holds that ‘[i]t is widely accepted that outside interference in favour of one party to [a civil war] permits counter-intervention on behalf of the other’.Footnote 210 Such a counter-intervention can be qualified in one of two ways. As explained above, if State support for non-State armed groups reaches a certain threshold, tentatively defined as the ‘overall control’ test, then the conflict is ‘internationalized’. This then provides the necessary ‘external’ component for purposes of identifying an ‘armed attack’ in the sense of Article 51 UN Charter, potentially triggering the right to (collective) self-defence.Footnote 211 Alternatively, if the foreign involvement of the NSAG is insufficiently grave to trigger the right of self-defence, it may nonetheless permit a third-State to intervene on the side of the de jure government on the basis of the ‘intervention by invitation’ doctrine.Footnote 212 Such intervention, it is argued, does not infringe upon, but rather seeks to uphold/restore, the right of peoples to freely determine their own political status without outside interference.Footnote 213
The concept of ‘counter-intervention’, while arguably the best established exception to the non-intervention principle, has proven particularly prone to abuse.Footnote 214 States have indeed on numerous occasions drawn the ‘counter-intervention’ card, in situations where the existence, and extent, of prior outside intervention in support of rebels was unclear. Leaving aside problems of proof, the question arises what degree of prior outside intervention is needed to justify a lawful ‘counter-intervention’ and whether some minimum degree of proportionality must exist between the two forms of third-State intervention. No clear answer can be derived from State practice or from the case law of the ICJ.
What is more, these questions have so far been largely overlooked in legal doctrine.Footnote 215 With regard to the threshold of application, the one thing that can be said with some certainty is that the initial assistance on the part of the non-State actor must at least be ‘likely to have a substantial impact’ on the outcome of the civil war.Footnote 216 On a related note, if the shipment of small arms and light weapons (or even financial support?) by one State to rebels in another country suffices to justify a ‘counter-intervention by invitation’ in support of the de jure authorities, is the latter not subject to a proportionality test? While it is beyond this article's scope to verify whether this position is actually reflected in State practice and opinio juris, given that recourse to self-defenceFootnote 217 or countermeasures is always subject to a proportionality requirement, and given that counter-interventions are also a form of self-help, normatively, a strong case can be made that this requirement should apply by analogy.Footnote 218
The impact of the right of self-determination arguably points in the same direction. Indeed, counter-intervention could be said not to contravene the right to self-determination if it is in proportion to the original extent of outside assistance. Put differently, counter-intervention should be about undoing the impact of the original intervention on the side of the rebel groups—it should be about evening the odds, not tilting the balance in favour of the de jure authorities. Any other interpretation would arguably strip the prohibition as discussed so far of all meaning. In practical terms, if counter-intervention were not deemed subject to a proportionality requirement, this would imply, for instance, that third-State arms deliveries to moderate rebels in Syria (in 2013–14) would permit the Assad regime to seek direct outside military support to crush the rebel presence.
If it is accepted that ‘counter-interventions’ are subject to a proportionality test, it is highly questionable whether the States intervening in the Yemeni crisis can fall back on alleged Iranian interference to justify Operation Decisive Storm/Renewal of Hope. As described above, Iran has been accused of fostering a relationship with Houthi rebels by providing political and material support (ie, arms deliveries and military training).Footnote 219 However, the full-blown Saudi-led military campaign was clearly excessive in relation to the Iranian support, even if all rumours thereof are accepted as fact. Saudi Arabia had taken charge of a military operation involving approximately 200 aircraft, 18 warships, and 150,000 combat troops along the border.Footnote 220 Leaving aside the humanitarian catastrophe that occurred due to the outbreak of hostilities,Footnote 221 these military operations were thus hardly proportional to the ‘mere’ provision of arms and military training. In conclusion, strong doubts remain over the legality of the Saudi-led operation.
Finally, apart from referring to alleged prior Iranian support to the Houthi rebels, during the UN Security Council debate, a number of States also linked their support for the legitimate government to their disapproval of ‘spoilers’ in Yemen's transitional process.Footnote 222 In a similar vein, Security Council resolution 2216 ‘[e] xpress [ed] alarm that … actions taken by the Houthis undermine[d] the political transition process in Yemen, and jeopardize[d] the security, stability, sovereignty and unity of Yemen’.Footnote 223 In other words, could it be argued that the military intervention against the Houthi rebels, perhaps indirectly, promoted, rather than undermined, the Yemeni people's right to self-determination?
Upon closer consideration, the idea that an intervention in support of one party to a civil war can, depending on the circumstances, be seen as supportive of the right of self-determination, and therefore be regarded as lawful, is deeply problematic. First, the Friendly Relations declaration expressly prohibits ‘external interference’ in the exercise of a people's right to ‘freely determine … their political status’.Footnote 224 There is thus an immediate and inherent contradiction in a foreign military intervention to restore the right to self-determination (unless, perhaps, it constitutes a proportional counter-intervention as discussed in the previous paragraphs). Ultimately, paraphrasing Lauterpacht, to allow military intervention on the side of one party to a civil war would ‘amount to … a denial of the right of the nation to decide … – by a physical contest if necessary … – the nature and the form of its government’.Footnote 225 In this context, one might also object that upholding/restoring the Yemeni's right to freely decide their future was not at the core of Saudi operations. Rather, these operations seemed to want to forcibly make that decision for them.
Furthermore, there is scarce support for such intervention in legal doctrine and State practice. Direct military intervention in support of ‘national liberation movements’ has always remained highly controversial—and is moreover by and large a thing of the past.Footnote 226 Beyond the colonial context, there is even less support for the legality of unilateral military intervention. For example, in relation to the (potential) right to self-determination of South Ossetia and Abkhazia, which was one of the arguments mentioned (but not, in the end, relied upon) by Russia in relation to its military intervention in Georgia,Footnote 227 the International Fact-Finding Mission on the Conflict in Georgia subsequently found that:
[m]ilitary force is never admissible as a means to carry out a claim to self-determination, including internal self-determination. There is no support in state practice for the right to use force to attain self-determination outside the context of decolonization or illegal occupation.Footnote 228
On a closely related note, although there is some support in legal scholarship for so-called ‘pro-democratic’ intervention by invitation,Footnote 229 this position remains the minority view and finds little support in actual State practice.Footnote 230 Typically, the case of the ousted Haitian President Aristide is cited in support.Footnote 231 However, as discussed above, the intervention on his behalf was sanctioned by the Security Council.Footnote 232 More generally, whether one looks at the US intervention in Panama in 1989 or the US-led military intervention in Iraq in 2003, States have generally refrained from advancing the ‘pro-democratic’ character of an intervention as an autonomous legal justification.Footnote 233 According to Gray: ‘the political goals underlying the use of force may include the re-establishment of “democratic” government, but this has not led states to espouse a legal doctrine of ‘pro-democratic’ invasion without UN authority’.Footnote 234 What is more, even proponents of pro-democratic interventions upon request admit that in ‘the case of a full-scale civil war … an external intervention on behalf of the “democratic” forces … may reasonably be treated as an improper interference with the right of the State's people to determine its own future’.Footnote 235
This is sound. To enable third States to intervene on the side of the party which they perceive as being endowed with the greater degree of legitimacy would open the floodgates to unilateral military operations in non-international armed conflicts and fundamentally undermine the monopolization of the use of force in the collective interest in the hands of the UN Security Council. In the end then, the case of Yemen can thus not be legitimized by the (controversial) theory of ‘pro-democratic’ interventions.Footnote 236 Nor, in all fairness, did the intervening States display any intent to create a precedent in support of ‘pro-democratic’ intervention or intervention to support the right of self-determination. It follows that the intervention hardly qualifies as a precedent supporting any development de lege ferenda of a right to engage in intervention to promote democracy and/or self-determination.
VI. CONCLUSION
Although some States expressed reservations about the permissibility or desirability of the operation, the large-scale Saudi-led intervention in Yemen in the Spring of 2015 was met with approbation by the League of Arab States, by the US and the UK, and generally met with tacit approval from the international community as a whole.
In spite of this, and as explained above, the right of self-defence, which was put forward by the intervening countries as the primary justification for the operation, does not provide a credible legal basis. First, while there were indications of Iranian involvement on the side of the Houthi rebels, the degree of external involvement prima facie appears insufficient to transform the Houthi ‘aggression’ into an armed attack in the sense of Article 51 UN Charter justifying recourse to collective self-defence in support of Yemen. Second, absent an ‘imminent’ threat of armed attack, let alone an actual armed attack, by the Houthi rebels against Saudi Arabia, the operation can hardly be construed as an exercise of individual self-defence by the latter country.
Reliance on the doctrine of ‘intervention by invitation’ cannot go unchallenged either. First, while Operation Decisive Storm was preceded by a request for military assistance from Yemeni's beleaguered President, one cannot ignore that he had lost control over a considerable part of Yemeni territory (and actually fled to Saudi Arabia mere days after the request). Regardless of this, however, the Hadi government continued to enjoy broad international recognition, with no State expressly questioning the validity of Hadi's request. The tentative lesson to be drawn from this is that, for purposes of assessing the validity of a request for military assistance, the degree of international recognition can compensate for substantial loss of control over territory. One point of concern here is that international recognition is a fickle barometer and inevitably introduces an element of subjectivity in the application of the legal framework: force may be legal in one scenario and illegal in a factually very similar one, depending on the attitude of the international community.Footnote 237
Second, even if one accepts that Hadi could validly express the will of the Yemeni State, the Saudi-led intervention undeniably interfered with the civil strife within Yemeni territory between Hadi loyalists and Houthi rebels. This aspect puts the operation at odds with the principle of non-intervention, read in conjunction with the right of self-determination. Critics of the ‘negative equality’ doctrine will simply regard the Yemeni precedent as yet more evidence in State practice that the former doctrine is dead, and are supported by the international community's meek reaction to the launch of the intervention. Proponents of the doctrine may object that the Yemeni intervention is simply an application of the concept of ‘counter-intervention’, as the doctrine's best-established exception, pursuant to prior Iranian intervention on the part of the Houthi rebels. As such, they may argue that it leaves unaffected the general point of departure that intervention by invitation is ‘normally’ excluded in civil war settings.
Yet, unless it is subject to some de minimis threshold and, more importantly perhaps, a proportionality test, the concept of ‘counter-intervention’ is little more than an empty shell—and the difference between the two approaches may be a mere exercise in semantics. Indeed, assistance to non-State armed groups in the form of financial assistance, provision of weapons, or even military training, is regrettably widespread and has been on the rise ever since the Arab spring revolts. In addition, accusations of such assistance are easily concocted. If any such assistance suffices to permit a large-scale third-State intervention, it is hard to see what would, for instance, prevent the Assad regime from inviting foreign troops to fight rebel groups on its soil, etc. Although this question has been largely overlooked in legal doctrine, it is argued that counter-intervention should indeed be subject to a proportionality test. Furthermore, if this is the case, strong doubts arise over the legality of the Saudi-led operation.
Operation Decisive Storm is the latest in a series of recent military interventions that are justified at least in part by reliance on the intervention by invitation doctrine. It again illustrates the indeterminacy of this doctrine and the risk of abuse. It further illustrates that State practice has yet not produced a uniform, clear and objective test to determine who has the right to invite outside intervention, and under what conditions. In the end, by failing to have the operation sanctioned by the UN Security Council, the intervening States (and the States approving of/condoning the operation) have undermined the primary role of the UN Security Council for the maintenance of international peace and security, and set a dangerous precedent.
