Mark Ellis is the Executive Director of the International Bar Association (IBA). He served as Legal Advisor to the Kosovo Commission and advised the OSCE on the creation of Serbia's War Crimes Tribunal. Dr Ellis worked alongside the ICTY, the Iraqi High Tribunal, the Cambodia Tribunal and presently with the ICC. In 2015, he was appointed to the UN Advisory Panel on Defence Counsel and in the same year launched eyeWitness to Atrocities, a mobile app for documenting war crimes. Since Russia's invasion of Ukraine, Dr Ellis has led the IBA's support efforts for Ukraine and, as a result, has been sanctioned by the Russian government. He was awarded Ukraine's order of merit, one of Ukraine's most distinguished state honours conferred by the President. His latest book, The UN Charter: Five Pillars for Humankind (Springer 2025), is co-authored with Ambassador David J Scheffer.
Where do you see the most exciting research/debates happening in your field?
One of the most important developments in international law is the increased use of universal jurisdiction. Universal jurisdiction is the idea that atrocity crimes, such as war crimes, genocide and crimes against humanity, are an affront to the world and every state can, and arguably must, prosecute these crimes. This is different from standard forms of jurisdiction, such as those based on the location of the acts or the nationality of one of the parties. There is an increased push to use universal jurisdiction, with over 50 cases open in 14 countries using absolute universal and over 100 more across 6 additional countries using either active or passive personality. In the last year, universal jurisdiction has been used by Finland to convict a Russian paramilitary leader for acts in Ukraine in 2014, and in Germany, Netherlands, and the United States against numerous former Syrian officials. Universal jurisdiction is not perfect, states are hesitant to risk overstepping their legal authority and there are difficulties gaining custody, but it provides a pathway towards justice where it otherwise has been denied. Even the threat of universal jurisdiction has an effect, limiting where those accused of serious crimes can freely travel without concern.
How has the way you understand the world changed over time, and what (or who) prompted the most significant shifts in your thinking?
The most dramatic change in my understanding of world affairs has been the rise of populism and nationalism. This phenomenon has emboldened the arbitrary exercise of state power. We are witnessing populist leaders targeting anything that criticises or constrains their authority. As a result, populists attack the media, the bureaucracy, universities, the judiciary, and civil society. Much of this is driven by loyalty to a populist leader who employs anti-establishment rhetoric to amplify perceived losses of cultural identity and economic security. Populists rail against multiculturalism, presenting themselves as the sole defenders of the “ordinary people.†Often, the populist leader is also a nationalist leader, characterised by an “us versus them†mentality and frequently accompanied by xenophobia, venomous intolerance, and the weaponisation of hatred toward others. The rise of both populism and nationalism over the past decade has been dramatic, and to me, deeply troubling.
You have described the UN Charter as “the world's most important secular document.†At its core lies Article 2 and the prohibition of the use of force against the territorial integrity and political independence of states, a principle closely tied to the crime of aggression. At a time when this principle appears to be increasingly contested, how critical is the prosecution of aggression to the survival of the post-1945 international order?
I recently wrote in Just Security, that when the framers of the United Nations Charter enshrined Article 2(4) at its adoption in 1945 in the wake of the Second World War, they established one of the most enduring principles of modern international law. It provides: “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.â€Â Those 38 words capture the essential objective of the Charter. The STCA, therefore, stands as the bridge between the Charter's aspirational promise and the practical reality of holding accountable those who choose to violate it. The Charter established the prohibition against the crime of aggression; the STCA is the mechanism through which this prohibition is finally given effect. And there is no clearer example of the crime of aggression than Russia's February 2022 invasion of Ukraine. Thus, the STCA seeks to close one of the most enduring gaps in international criminal law and, in doing so, complete the trajectory that began with Nuremberg and with the promulgation of the Charter itself. Â
The International Bar Association has played a prominent role in advancing the idea of a Special Tribunal for the Crime of Aggression against Ukraine, which has now taken concrete institutional and legal form. Yet this reveals a deeper paradox: in order to uphold the UN Charter's prohibition on aggression, supporters of the tribunal have effectively had to act outside the UN system itself, due to Security Council paralysis. Do you see this as a sign of institutional resilience or of a deeper crisis in the post-1945 collective security order?
Both. The resilience of the UN Charter can be seen in the fundamental concept of justice; it encourages a concept that is core to the STCA. International law has revolutionized itself several times in search of an efficient system of justice, from Nuremberg to the ad hoc tribunals like the ICTY and ICTR to the independent investigatory mechanism such as the Independent Investigative Mechanism for Myanmar (IIMM) and the International, Impartial and Independent Mechanism for Syria (IIIM). The function of the STCA is similar to past ad hoc tribunals; a new approach to the same sense of justice and order. But at the same time, international law has been at a standstill for a while. While the ICTY and ICTR were effective in pursuing justice and creating lasting peace, both were created following the collapse of the Soviet Union where there was a willingness from the Security Council to experiment. This willingness no longer exists. Other entities such as the ICC are doing what they can to fill the gap, but the creation of the STCA will allow an additional approach to the promises of the UN Charter.
Discussions surrounding the Special Tribunal are taking place in a highly fluid geopolitical environment, where the pursuit of peace may come into tension with demands for international criminal accountability. At the same time, proposed peace frameworks advanced by key actors in the Russia–Ukraine negotiations have included provisions for broad amnesty. How can a project such as the STCoA survive in a political environment where justice is often treated as negotiable?
The political influence in international law is worrying. If politics denies justice to the victims of the war, then law has failed. However, this should not undermine our collective conviction in the dedication of peace and justice that underlie international laws. Any proposed peace settlement that does not provide justice is non-negotiable. Justice is something that must continue to be fought for in all forms, and the STCoA is an important part of that.
A common criticism of international justice is that it often appears either elusive or painfully slow. Yet the STCoA has seen an unusually rapid level of political and institutional mobilisation. To what extent does this reflect the importance of collective political will, strategic legal mobilisation, and the relationship between international institutions and affected communities in making international justice possible today?
We must acknowledge the reality that politics play a role in the implementation of international law. International law is at the tension point between the competing desires to implement a universal standard of international law and the political desire to advance national interests. While we must be wary of the influence of these factors, there can also be benefits where positive political will can be used to advance international law and establish norms. The Nuremberg trials were supported by the political widespread will, and it laid the groundwork for international law going forward. A similar statement can be made for the ICTY and ICTR. This is where strategic legal mobilization comes in: international law can garner support for popular or desired projects and use them to get the legal precedent to universally address all situations in the future. This is not a call for selective justice – all wrongs must be legally pursued and advocated against strongly – but by beginning with the widely condemned crimes, the political roadblocks could be lessened in the pursuit of universal justice. The crime of aggression has not been since Nuremberg prosecuted, and the political desire to investigate Russia can be the groundwork for activating this crime. The relationship between international institutions and the affected communities is especially important because of the role political will plays in jumpstarting or slowing down international procedures. While political mechanisms may be slow to support new initiatives due to political inertia, the affected communities will have great interest from the start. This interest can complete much of the legwork in collecting evidence and documentation.
One of the most persistent criticisms of international criminal justice is that it often appears selective, shaped by geopolitical power. In the case of the STCoA, some have noted that several states supporting the tribunal were also involved in the 2003 invasion of Iraq, which did not lead to comparable accountability efforts for aggression. How can the tribunal avoid reinforcing perceptions of selective justice?
The perception of double standards is arguably the greatest existential threat to the legitimacy of international criminal law. When states that championed or participated in the 2003 invasion of Iraq (an action widely criticized as a violation of the UN Charter) become supporters of a new tribunal like the STCA, scepticism is both predictable and justified. To avoid reinforcing these perceptions of selective justice, the tribunal cannot be seen as an instrument of victors' justice or geopolitical convenience; it must be grounded strictly in principles that apply equally to all sovereign actors, regardless of their geopolitical alignment, aligning with the rigorous standards outlined in widely accepted legal standards that are embedded in the UN Charter.
The tribunal appears to adopt a cautious approach to the personal immunities of sitting state officials, avoiding a direct confrontation with the logic of the ICJ's Arrest Warrant judgment. At the same time, this leaves some of those most responsible beyond its immediate reach. Does this strengthen the tribunal's legal viability, or reveal the deeper limits of international criminal justice?
The decision to respect the traditional boundaries of personal immunity for sitting state officials – realigning with the logic of the ICJ's landmark Arrest Warrant Judgment – is a calculated compromise. It represents a pragmatic choice to prioritize legal viability over immediate, comprehensive accountability. By respecting the immunities of sitting heads of state and foreign ministers under customary international law, the tribunal shields itself from accusations of judicial overreach and ensures broader state cooperation. In a fragmented global order, a court that lacks enforcement mechanisms cannot afford to alienate the very state apparatuses it relies upon to execute warrants and gather evidence. However, this caution undoubtedly exposes the painful, inherent limits of the international legal order. It creates a paradigm where those holding the highest levers of power remain temporarily untouchable, leaving a gap between the aspiration of universal justice and the reality of state sovereignty. This does not mean the tribunal is toothless, rather, it shifts the strategy to a long-term game.
You describe the UN Charter as a “vibrant document of hope and vision†despite growing geopolitical fragmentation and pressure on universal norms. Yet the UN enters its 80th anniversary amid Security Council paralysis, financial strain, and a broader crisis of multilateralism. What is the greatest challenge facing the UN system today, and how can the normative achievements of the post-1945 order still be defended realistically?
The greatest challenge facing the United Nations system today is not structural paralysis or financial strain, but a fundamental crisis of trust and compliance among its most powerful members. As the UN recently celebrated its 80th anniversary, the paralysis of the Security Council, driven by the frequent use of the veto by P5 members, has severely undermined its primary mandate to maintain international peace and security. When the very custodians of the UN Charter bypass or violate its core normative tenets, the fabric of the post-1945 order is stretched to its absolute limit, fostering a dangerous cynicism about the efficacy of global governance. Defending these normative achievements realistically requires moving past romanticized expectations of the UN and focusing on its resilience. The defence of international law is increasingly shifting away from a frozen Security Council toward the UN General Assembly, regional coalitions, and specialized international courts. The STCA is one of those new mechanisms.
Many students, young scholars, and practitioners in International Relations and International Law feel deep cynicism and disappointment about the effectiveness and consistency of international institutions and legal norms. How can these fields retain their legitimacy today, and what would you say to those who question whether they are still worth studying and defending?
The cynicism felt by young scholars and practitioners today is a clear-eyed response to a world where power frequently trumps principle. It is entirely understandable to question the utility of international law when compliance appears optional for the powerful. However, the legitimacy of these fields is maintained precisely because international law is not a static system of enforcement, but a continuous site of political struggle. Without the framework of international law, the alternative is a return to unmitigated raw power, where the weak have no recourse whatsoever. To those questioning whether these disciplines are still worth defending, I would point to milestones like the Universal Declaration of Human Rights, which demonstrate that international law is most critical precisely when it is most challenged. Every major advancement in human rights, state accountability, and global cooperation was born out of crisis and perceived failure. Legal norms provide the essential architecture for future reform and the standard by which injustice is measured and condemned. Studying and practicing in these fields is not an exercise in idealism but is a necessary commitment to holding power to account and tilting the global balance toward justice.
Further Reading on E-International Relations
