The case concerning Military and Paramilitary Activities in and against Nicaragua,Footnote ¹ better known as the ‘Nicaragua case’ or simply Nicaragua, is arguably one of the most important and controversial cases ever to be heard by the International Court of Justice.Footnote ² Twenty-five years after the judgment on the merits was handed down, it is high time to reassess the impact of Nicaragua on international law.Footnote ³ The joint efforts of the Grotius Centre of the Leiden Law School, the Centre on International Courts and Tribunals at University College London, the Netherlands Society of International Law, and the law firm Foley Hoag LLP resulted in a one-day conference, on 27 June 2011, the very day on which the judgment on the merits of the Nicaragua case was handed down, 25 years ago.

By fortuitous circumstances, this year marks the 25th anniversary of the Leiden Journal of International Law.Footnote ⁴ Accordingly, it seemed fitting to the editors of this journal to commemorate both occasions by publishing the proceedings of the conference. The editors are grateful to those speakers who accepted the invitation to publish their contributions, which will appear in the current and following issues.

Even after 25 years, international lawyers can get unusually emotional when discussing particular issues dealt with by the Court, not only in its 1986 judgment on the merits, but also in the equally controversial 1984 judgment on jurisdiction that notoriously resulted in the United States of America retracting its optional clause declaration accepting the Court's jurisdiction.Footnote ⁵ The fact that the Nicaragua case is present in so many legal discussions and has been referred to in numerous subsequent judicial decisions is due to not only the outcome of the case, the participation of a ‘superpower’, or even its political implications. The Court's pronouncements in that case are significant in that they confronted almost all of the most important issues of the international legal order at the time. It is therefore not surprising that Nicaragua became a major reference for international lawyers. Indeed, the case could serve as a textbook for an ‘Introduction to Public International Law’.Footnote ⁶

The case posed, first of all, existential questions on the law and procedure of the Court (the mechanism of declarations recognizing the Court's jurisdiction and their relationship with compromissory clauses, the effect of reservations to such declarations, the scope of the Court's jurisdiction, etc.), but also on the very role of the judiciary in international dispute settlement, especially in those disputes that are considered to be more of a political than of a legal nature, as required by Article 36(2) of the Court's Statute. The Court had also to decide on several issues relating to the proceedings before it, including the establishment of the consent of a state to its jurisdiction, the indication of provisional measures, the admissibility of a request for intervention,Footnote ⁷ and the problem of the non-appearance of the respondent party in the merits phase of the case.Footnote ⁸ For this reason, the judgment on the merits also contains significant developments regarding the fact-finding powers of the Court and the principle jus novit curia, among many others.

The case further led the Court to deal with a wide range of substantive issues. These included, for example, fundamental questions regarding the sources of international law, reservations to treaties, the establishment of the existence of a customary rule of international law, and the relationship of customary international law and treaty law. In its judgment on the merits, the Court also dealt with the principle of non-intervention and the scope of application of the rules of international humanitarian law, as well as matters relating to humanitarian assistance. It made significant pronouncements on the classification of armed conflicts and on the obligations under common Article 3 of the Geneva Conventions. The judgment further contained momentous findings on the rules relating to the prohibition of the use of force in international law, both within the system of collective security designed by the Charter of the United Nations and in customary international law, and it remains a landmark decision in this area. The Nicaragua judgment was equally groundbreaking in the field of state responsibility, both crystallizing the achievements of the first phase of the works of the International Law Commission and providing food for thought in a debate that continues – in many respects – even today, most notably with respect to the attribution to the state of conduct of paramilitary entities and the famous criterion (which has now become famous as the ‘Nicaragua test’) of ‘effective control’.

In view of the breathtaking range of topics considered by the Court, it is not surprising that, in its 25 years of existence, there has been a backlash against certain of the conclusions reached in Nicaragua. Most famously, the Appeals Chamber of the International Criminal Tribunal for the former Yugoslavia in 1999 cast doubt on the ‘effective control’ test applied in the Nicaragua judgment,Footnote ⁹ which led the Court to revisit the matter in the Genocide (Bosnia and Herzegovina v. Serbia and Montenegro) case in 2007.Footnote ¹⁰ A second backlash took place in the context of the ‘war on terror’, which triggered discussions in political circles and academia on the seeming death of Nicaragua.Footnote ¹¹ Exchanges such as these, catalysed by the Court's pronouncements in Nicaragua, have fed the international legal debate and thought in academic circles for years, and have raised in turn more general, systemic, questions relating to the so-called ‘fragmentation’ of international law,Footnote ¹² to the authority of the International Court of Justice as the principal judicial organ of the United Nations in a legal environment witnessing the proliferation of international tribunals, or even to the role of the law in international relations.

The Nicaragua case is considered to be the leading case of the International Court of Justice – a ‘milestone’, as Professor Kohen puts it.Footnote ¹³ Even outside the jurisprudence of the Court, Nicaragua ranks amongst the most important cases decided in the past century.

For all these reasons, the editors of this journal are delighted to publish several contributions to the conference that reflect on the influence of the judgment and its lasting relevance for the perception of international law and dispute settlement today.