War is changing. The conflicts raging in shattered places across the globe today differ markedly from their historical antecedents in terms of the participants, the manner in which armed conflicts are fought, and their purpose. With the rapidity of technological and social change, this dramatic evolution will continue. As military historian Sir Lawrence Freedman wrote, “There is no longer a dominant model for future war, but instead a blurred concept and a range of speculative possibilities.” But have the international legal rules that the world should apply to these conflicts changed with the nature of the conflicts they seek to regulate?

A tragic example of the complexity of modern conflict is the situation in Syria – a maelstrom of monstrous brutality, characterized by myriad competing groups and countries with clashing geopolitical objectives. In the chaos, international law seems to wane, receding into the background and losing its normative force.

Since the inception of the Syrian conflict in 2011, the world has witnessed a murderous regime commit a range of crimes against civilians, including “shelling, chemical weapons attacks, barrel bombs, airstrikes, arbitrary detention, torture, and starvation,” as the United States and allies described in a joint statement earlier this year. Likewise, other nation states have carried out military operations on Syrian territory, including air strikes by the United States, Russia, and Iran. The actions have spurred near-constant debate on the legality of the use of force in such circumstances as well as the need for accountability for violations of international law. And beyond the discussions centered on bombs, bullets, and military activity are the myriad concerns associated with displaced persons, refugees, and migrants.

In the book “The Syrian Conflict’s Impact on International Law,” noted international law experts Michael P. Scharf, Milena Sterio, and Paul R. Williams present a uniquely comprehensive effort to explain the war and the international legal rules that purport to govern the activity of most of the actors on the Syrian battlefield (nation-states, armed opposition groups, terrorist groups, etc.). The book successfully reaches beyond the single conflict and explicates how international law is evolving in this era of “new wars.”  In addition to providing readers with one of the most useful histories and elucidations of the key events in the Syrian conflict, the authors offer an insightful view of its impact on international law. They posit that the conflict has rapidly crystallized new international legal rules and significantly altered previous international approaches in classic “Grotian moments.”

Grotian Moments

Hugo Grotius, a noted Dutch scholar and diplomat of the 16th and 17th centuries, is a giant in the pantheon of international legal luminaries. Grotius was a practicing international lawyer early in his career, and is considered the father of modern international law due to the impact of his writing on the concepts of sovereignty, armed conflict, and the international legal order.

Due to the profound impact of his work, the term “Grotian moment” has appeared in international legal scholarship for several decades, and has been subjected to various meanings, usually denoting a transformative moment in international law or the world order. For instance, former United Nations Secretary-General Boutros Boutros-Ghali used the term to refer to “a renaissance of international law” that serves to “transform the world scene[.]”

Similarly, in previous scholarly works, two of the authors of this book have discussed the idea of a “Grotian Moment” as a “paradigm-shifting development in which new rules and doctrines of customary international law emerge with unusual rapidity and acceptance.”  The authors use this concept as a leitmotif to present certain “transformative events that accelerate the formation of customary international law or occasion significant interpretive changes of the UN Charter[.]”

A Historical Timeline

The book opens with a historical timeline that helpfully guides the reader through the evolution of the conflict. The authors divide the conflict into five phases: (1) a nascent stage marked by the beginning of the socio-political upheaval of the Arab Spring in 2011; (2) the outbreak of armed insurgency, which ripened into civil war in 2012 and saw the early intervention of Iran in 2013; (3) the rise of ISIS and the declaration of the caliphate in 2014; (4) the intervention of Russia in 2015 and the adjustment of U.S. strategy from countering ISIS to containing Iran; and (5) the reassertion of power by the regime of Bashar al-Assad beginning in 2016. The background chapter closes with a brief explanation of the operative legal frameworks – the law of armed conflict and international human rights law.

The book then delves into customary international law and sets forth its central legal premise: that the process of creating customary international law can be greatly accelerated or even instantly crystallized under certain circumstances, such as during armed conflicts. A primary example of such a moment is the Nuremberg Charter and the judgments of the Nuremberg tribunals. This chapter also (quite helpfully) draws from the experience of co-author Michael P. Scharf’s work in the Extraordinary Chambers in the Courts of Cambodia (EEEC) to establish that the concept of a joint criminal enterprise existed as a principle of customary international law. By weaving together the historical, theoretical, and practical, the book succeeds in providing a cogent explanation of how customary international law can rapidly form in certain unique circumstances.

The Law of Armed Conflict and the Use of Force

The book’s strongest examples of “Grotian moments” are those addressing the law of armed conflict and the use of force. The chapter on the use of force in self-defense against non-state actors is particularly illuminating, providing general background on the topic and demonstrating the way international law on this subject is being altered by contemporary counterterrorism operations, most notably, in the Syrian conflict. This chapter also provides what is the book’s most dramatic example of a “Grotian moment.”

The authors note that the international law of self-defense, as envisioned in Article 51 of the U.N. Charter, has been shaped by rulings from the International Court of Justice (ICJ). One example is the 1986  decision in Nicaragua v. United States of America, which held, among other things, that only “the most grave forms of the use of force” constitute an armed attack. The authors also highlight the aspects of that decision – and the line of ICJ decisions such as the Oil Platforms decision (Islamic Republic of Iran v. United States of America); Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda); and the Wall Advisory Opinion (Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory).  This string of decisions demonstrates the ICJ’s consistent jurisprudence, which finds that using force against a terrorist organization whose conduct is not imputable to the territorial state would constitute an unlawful attack.

From that baseline, the authors walk through a gradual evolution in national security that has required military responses against non-state actors and the U.S. position that it is now lawful to attack non-state actors (specifically terrorist groups) when they are present on the territory of a state that is unwilling or unable to effectively address the activity of the terrorist group. The authors provide a lucid, informative discussion of post 9-11 national security responses, culminating in the multilateral coalition that participates in the Syrian conflict as well as U.N. Security Council Resolution 2249, which, the authors write, “will likely be viewed as confirming that the use of force in self-defense is now permissible against non-state actors where the territorial state is unable to suppress the threat that they pose.”

The chapter, thus, provides an informative and digestible discussion of international law as it relates to the use of force against non-state actors. But it also effectively supports the book’s contention that the conflict in Syria provided an environment for  “Grotian moments” that have quickly and definitively altered the state of the law in this complex (yet increasingly important) area of international law.

The chapter on humanitarian intervention, in turn, examines whether the military strikes taken against Syria on April 24, 2018, were a “Grotian moment” that created or altered customary international law as it relates to the use of force. These airstrikes were launched by the United States, the United Kingdom, and France against “Syrian chemical weapons facilities in response to a chemical weapons attack in a Damascus suburb[.]” In analyzing the international legal implications, the book walks the reader through the modern history of humanitarian intervention, starting with the 1999 NATO air strikes against Serbia that were undertaken in order to prevent the ethnic cleansing of Kosovar Albanians. The authors contend that those strikes could not create a new rule of international law justifying humanitarian intervention because key decision makers at that time, such as then-Secretary of State Madeleine Albright, described the action as “a unique situation sui generis in the region of the Balkans.”  Accordingly, the potential “norm pioneers” – to the extent there were any – were never clear in their articulation of a new rule.

Relatedly, the authors also demonstrate how the nascent doctrine of Responsibility to Protect (R2P) never fully ripened into customary international law because of the plurality of competing definitions and interpretations to which it was subject. One example is the meaning articulated in December 2001 by the International Commission on Intervention and State Sovereignty (ICISS), which stressed the need for authorization by the U.N. Security Council or, in the alternative, the U.N. General Assembly and, to a limited extent, regional or sub-regional organizations.

Against this backdrop, the book posits that the 2018 allied airstrikes in Syria were distinctive as a collective military action, taken outside the ordinary U.N. Security Council framework, for which the legal rationale articulated by participating countries (including the United States) was that of humanitarian intervention. Moreover, the book highlights the broad international support for the 2018 airstrikes, the very few and predictable voices of opposition, and the fact that the actions were taken in order to vindicate a peremptory norm of international law (jus cogens ) – to stop the use of chemical weapons against the civilian population. Given these factors, the authors convincingly assert that the 2018 allied military strikes against Syria were a “Grotian moment” that hardened the customary international rule justifying humanitarian intervention.

New Paradigms in Policy

The remaining chapters mainly address topics related to new paradigms in policy and international institutions that were forged in the midst of the Syria crisis. The book’s chapter on accountability describes the efforts of “custom pioneers” like Christian Wenaweser, formerly Liechtenstein’s ambassador to the U.N., that eventually lead to the creation of the International, Impartial, and Independent Mechanism to Assist in the Investigation and Prosecution of Those Responsible for the Most Serious Crimes under International Law Committed in the Syrian Arab Republic since March 2011 (the IIIM). This mechanism, designed to investigate and collect evidence related to international crimes committed in Syria,  was the first example of such an investigative body to be created by the U.N. General Assembly rather than the Security Council. As the authors note, this development (taken in response to the Security Council’s perennial paralysis) was a Grotian moment in that it was a shift in power from the Security Council to the General Assembly and could presage how similar institutions are developed in the future.

Similarly, the chapter on refugees and migrants demonstrates how the Syria crisis has pushed some countries – notably Germany and Turkey – to abandon asylum-based approaches and adopted novel resettlement policies that give protected status that better permits such persons to seek employment, integrate, and contribute economically to the host nation. While this seems more like a significant policy impact than a Grotian moment, it remains a noteworthy shift in approach to a major issue, and the change was spurred by the conflict in Syria.

The book’s final chapter provides what is perhaps the most detailed and insightful history of the Syrian peace process in contemporary literature.  This detailed review examines its origins in an effort undertaken by the Arab League (a regional international organization in the Middle East) and follows its evolution to the U.N. General Assembly, and finally to the U.N. Security Council. This process produced a novel approach of “annexing the framework and stipulating the outcome objectives in subsequent resolutions[.]” While this seems more of a procedural innovation than a substantive legal development,  the authors contend the model followed in creating the legal framework for the Syrian peace process will likely become a trend in future peace negotiations.


The Syrian Conflict’s Impact on International Law” stands out as an essential text and resource for scholars, practitioners, and policymakers seeking an in-depth understanding of the Syrian conflict and the related international legal issues. It masterfully explains international law as it relates to complex conflicts, but also defines several instances in which new rules and doctrines of customary international law have rapidly emerged. It also highlights several cases of key policy changes that emerged from the Syrian conflict.

Still, this is not merely a book about Syria and international law; it is a book with a more expansive vision and insight about how international law is being created in an evolving world order of uncomfortable asymmetric multipolarity, with new kinds of wars and conflicts that proceed according to a different method and logic. It is also a world order characterized by new threats and institutional obstacles (such as a sclerotic and ineffective U.N. Security Council). To reconcile international law with this new logic requires articulation of theories that adjust old rules to the new realities. The book demonstrates how States and other key actors have re-forged international norms to adjust to a rapidly changing global security environment, and describes a process of legal evolution that can help identify new norms in an increasingly volatile and complex world.

(The opinions expressed are not necessarily those of the United States Department of Justice or the Department of Defense.)

IMAGE: A medical staff member at Damascus Countryside Specialized Hospital holds a placard condemning a suspected chemical weapons attack on the Syrian town of Khan Sheikhun, during a gathering to show solidarity with the victims in the rebel-held Douma on the outskirts of Damascus on April 6, 2017. U.S forces fired a barrage of cruise missiles at a Syrian airbase on April 7 in response to what President Donald Trump called a “barbaric” chemical attack he blamed on the Damascus regime. (Photo by SAMEER AL-DOUMY/AFP via Getty Images).