The ways in which IHL, and states' understanding of their obligations under IHL, evolve and develop is also critical to the United States, and the ICC shapes and is being shaped by those developments. The United States has recognized that international criminal tribunals will inevitably influence the development of international law; for example, it submitted amicus briefs to the ICTY when important questions of law arose to help shape the development of the law and it has hailed the work of the ICTY as “establish[ing] key precedents in international criminal law.” ³⁴³ Given its mandate, the ICC will inevitably address a range of IHL issues in which the United States has an interest. For example, the judgment of the Appeals Chamber in Prosecutor v. Bemba addressed questions of superior responsibility, especially in the context of delegated and remote command over troops in coalition actions, ³⁴⁴ and questions of conflict classification (between government forces and an armed group receiving varying levels of foreign support) arose repeatedly in Prosecutor v. Lubanga. ³⁴⁵ The ICC’s decisions may also bear on other important international law issues—for example, the obligation to investigate and prosecute crimes associated with armed conflict, the grounds on which officials may enjoy immunity for conduct that allegedly constitutes international crimes, the reach of various forms of responsibility, and the circumstances in which a state may be held responsible for the conduct of armed groups to which it may wish to provide support. These issues touch on core U.S. foreign policy priorities, such as potential assistance to members of the moderate armed opposition in Syria and arms sales to the parties to the conflict in Yemen. The Court’s approach to these issues will inevitably influence the views of other members of the international community, particularly given that many states have updated their penal codes to include international crimes as defined by the Rome Statute and will inevitably look to the Court’s jurisprudence for interpretive guidance.

Separately, the ICC Assembly of States Parties may take actions that affect the views states have of their obligations under customary international law. For example, U.S. participation in the negotiations around amendments to the Court’s subject matter jurisdiction—adding the crime of aggression and several new war crimes in non-international armed conflicts—was in fact critical for helping to ensure that the outcome was compatible with U.S. positions. Future ASP discussions could well be expected to address such important emerging issues as cyberattacks and the responsibility for large-scale environmental damage under international law. The United States thus has a strong interest in ensuring that its voice and perspectives are present in these discussions, and that it does not cede this forum to other states whose interests or interpretations of the law may not be aligned with those of the United States.