The Factual and Intellectual History

The book is divided into five parts. Parts 1 and 2 provide the history of the incident itself and the diplomatic dispute that simmered for several years thereafter. Forcese clearly relishes the history for its own sake, but, as he emphasizes throughout, this history has a real significance precisely because it has been overly simplified and mischaracterized in the development of the law. Of particular importance is the fact that the insurgents had actually already occupied Navy Island on the Canadian side of the Niagara River, and had for some time been launching attacks into Upper Canada. They were preparing further attacks and were using the Caroline to ferry weapons, munitions, and men to the island from upper New York. Asked by the British to suppress local support for the insurgency and prevent the launching of attacks from within American territory, the US government was found to be “unwilling or unable to prevent aggression against Canada.”^{Footnote 4} In short, the strike on the Caroline was in response to actual armed attacks and an invasion of territory, and to prevent a further escalation of those attacks. This is hugely significant, given that the Caroline incident is typically cited in justifications for the validity of anticipatory self-defence.

It is also frequently forgotten that the diplomatic dispute simmered for several years and was only brought to a boil by the American arrest and prosecution of a Canadian for his alleged role in the raid. Remarkably, the trial threatened to provoke a war, and Daniel Webster’s famous dictum was issued almost four years after the raid in efforts to prevent further escalation. The issue was only resolved with the conclusion of the Webster-Ashburton Treaty ^{Footnote 5} in 1842, with an apparent agreement on Webster’s dictum and an agreement to disagree on its application to the facts.

Parts 3 and 4 then explore the intellectual history of the incident. Part 3 examines the merits of the arguments made by each side at the time, with Forcese briefly reviewing the history of international law on war up to the time of the Caroline affair. This foundation is used to support two important points: first, that there was at the time no legal prohibition on the use of force to achieve national policy objectives and, second, that there was a broad right of self-preservation to justify uses of force short of war, particularly against neutral states. Ironically, the United States had invoked this broad right of self-preservation to justify its own strikes into then Spanish Florida, in the first Seminole War of 1817–18, on the grounds that Spain was unwilling or unable to prevent attacks on the United States by Indigenous groups operating from within Spanish territory. Thus, Webster’s formulation of the concept of self-defence, and particularly its incorporation of the elements of imminence and proportionality, represented a significant narrowing of the scope of this right of self-preservation.

In Part 4, the book examines how the Caroline incident came to significantly influence the subsequent development of thinking about the use of force and self-defence. Forcese explores how jurists and scholars treated the Caroline incident in their writings, and how these writings influenced the development of the law from the end of the nineteenth century to the emergence of the modern jus ad bellum regime. As he notes, the concept of self-defence only becomes truly consequential when the use of force itself has been made unlawful. This general intellectual history will be familiar to many, and Forcese relies on such seminal works as Stephen Neff’s magisterial history of the subject.^{Footnote 6} But the account is necessary in order to explain the significance of the Caroline. Forcese’s examination of how the Caroline itself came to influence these developments is both fascinating and instructive, from the drafting history of Article 51 of the Charter of the United Nations (UN Charter) through to the seminal decisions of the International Court of Justice (ICJ) on the use of force.^{Footnote 7} Forcese’s book highlights how accounts of the Caroline incident were increasingly shorn of significant details over time and how the mischaracterization of events impacted the shaping of the law.

Analysis of the Current Issues

In Part 5, Forcese examines the current controversies over the precise scope of the doctrine of self-defence, and each of its constituent elements, and assesses its significance as a meaningful constraint on state practice. He also explores how the Caroline incident continues to be employed in these debates. As important and fascinating as the history is, many readers will likely be most interested in this analysis. Yet, if there is any quibble to be found with the book, it is that here Forcese could have drilled deeper. In particular, his analysis of the issues surrounding the nature of “imminence,” “armed attack,” and the efforts to expand self-defence with the “unwilling or unable” doctrine, could have benefited from a more detailed treatment — though, to be sure, this would have involved difficult trade-offs.

To explain this quibble, I must skip forward to the book’s conclusions as to the Caroline’s legacy. Forcese notes that the “constructive ambiguity” of the Caroline test has been exploited by states in efforts to broaden the scope of self-defence and even employed in pretexts for the unlawful use of force. There is of course considerable irony here, given that such efforts tend to shift the doctrine of self-defence closer to the broad right of self-preservation that Webster’s formulation sought to replace. Forcese thus concedes that the doctrine of self-defence has not been able to constrain the use of force as much as might be ideal. He concludes, however, that this flexibility may nonetheless be a strength. He refutes Antonio Cassese’s arguments for a sharper definition as being potentially counterproductive, given that a clarified doctrine would likely be undermined by increased violation.^{Footnote 8} He instead endorses Michael Reisman’s New Haven School perspective that “determinations of lawfulness in particular cases must … use a more comprehensive, consequentialist, and policy-sensitive approach,” positing that the Caroline test has survived so long precisely because it permits such an approach.^{Footnote 9} He concludes that the Caroline test and the doctrine of self-defence that it has shaped does indeed constrain state practice, even if it has sufficient flexibility and ambiguity to allow for evolution, which in turn results in debates over the doctrine’s scope and application. He frequently refers to Webster’s formulation as having been a pragmatic “Goldilocks formula,” and one is left thinking that Forcese similarly believes that, while not as effective as one might like, it is probably as effective as it can be. The problems created by its constructive ambiguity are the price we have to pay for this modest success.

A deeper analysis of some of these problems might have led to a less sanguine conclusion or, alternatively, to stronger normative arguments about the illegitimacy of recent efforts to distort aspects of the doctrine. To look at the element of imminence as one example, Forcese re-emphasizes how ironic and misguided it is that the Caroline test has come to be associated with anticipatory self-defence given the actual history of the incident. Recognizing that the language of Webster’s formulation does imply the permissibility of anticipatory action, he explains how it has been used to “lever open the scope of the ‘armed attack’ ‘occurs’ standard in Article 51” of the UN Charter.^{Footnote 10} He traces this evolution through to the debates surrounding the so-called “Bush Doctrine” of 2002, and the development of the more “elastic and flexible” treatment of imminence in the “global war on terrorism,” describing how the Caroline test has been deployed by all sides.

Yet, while emphasizing that imminence is the element that has been most misunderstood and exploited, Forcese does not explore in detail the full extent of that distortion. The Bush Doctrine has been widely rejected by the international community, but in the context of targeted killing and the unwilling or unable doctrine, the United States and several like-minded countries have embraced an interpretation of imminence that has gutted the concept of all temporal meaning. This reality is reflected in the US justifications for the killing of Anwar al-Awlaki, notably that “the condition that an operational leader present an ‘imminent’ threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future.”^{Footnote 11} The so-called “Bethlehem Principles,” which have come to embody the source and legitimate articulation of the unwilling or unable doctrine, take this distortion further, suggesting that imminence can mean something other than “immediate” or “impending” and, indeed, that there need be no specific evidence of where an attack will occur or the precise nature of the attack for it to be imminent.^{Footnote 12} In other words, the concept is something not only entirely divorced from the essential meaning of the word “imminence” but also very far from Webster’s “instant, overwhelming, no choice of means, no moment for deliberation.”^{Footnote 13} Bethlehem’s five factors for assessing imminence conflate the concept of imminence with the magnitude of risk; replace the immediacy of the threat with windows of opportunity for response; and confuse the overall issue with considerations from international humanitarian law.^{Footnote 14} While this distortion of imminence is designed to help justify the unwilling or unable doctrine as a narrow application of the broader doctrine of self-defence, there is a risk that its wider acceptance will alter the concept of imminence, and thus the principle of necessity more generally, and thereby lower the threshold for the use of force in all applications of the right of self-defence.^{Footnote 15}

Forcese does devote a full chapter to the unwilling or unable doctrine for, as he rightly emphasizes, the Caroline incident was in many ways the first modern articulation of this idea — that is, justifying the use of force against NSAs operating from within the territory of another state based on the host state being unable or unwilling to prevent the NSAs’ attacks.^{Footnote 16} But, while he questions the validity of recent claims that the doctrine’s current formulation has become customary international law, and gives voice to concerns about the risks of relying on a “fuzzy doctrine” such as the unwilling or unable doctrine, Forcese does not explore in detail the more specific and significant problems raised by the Bethlehem Principles or engage directly with the significant scholarly debate on the subject.^{Footnote 17} This is reflected again in his examination of the element of “armed attack” as a trigger for the exercise of self-defence. He does explore how the “gravity” threshold for an “armed attack” has come under pressure, and he does an admirable job of defending the established view. But he only notes in passing the “misgivings” created by the unwilling or unable doctrine claim that a number of small strikes, none of which are separately of sufficient gravity or scale, may cumulatively constitute an armed attack justifying a use of force in response.^{Footnote 18} What is more, the unwilling or unable doctrine creates an attribution problem for the element of armed attack. The ICJ has consistently held that a state may only use force in self-defence against NSAs within the territory of another state if the NSA attacks can be sufficiently attributed to that state, for which the state’s “substantial involvement” in the operations of the NSA must be established.^{Footnote 19} But the unwilling or unable doctrine effectively abandons this attribution requirement, thus creating further pressure for broadening the doctrine of self-defence; an issue that the book does not address.

Final Thoughts

These comments on the level of detail with which current controversies might have been addressed are mere quibbles with what is an altogether magnificent book. What is more, given that Craig Forcese is one of Canada’s pre-eminent scholars on the law relating to the use of force, armed conflict, and national security, we can be sure that the level of scrutiny was a considered choice rather than any oversight. It was likely a trade-off in an effort to balance the goals of recounting a rich factual and intellectual history of the Caroline incident, exploring the significance of its influence on the development of international law, and analyzing its continued operation as an effective constraint within the jus ad bellum regime. And Forcese achieves that balance wonderfully, all within a coherent narrative. It clarifies the history in ways that should help reduce the misuse of the Caroline incident and clearly demonstrates the continued significance and relevance of the Caroline test. As such, the book may play some role in making the doctrine that much more effective. What is more, the blend of history, theory, and analysis, makes it a true pleasure to read — an important work of international law theory and intellectual history wrapped up in a military and diplomatic history of a swashbuckling affair.