Perhaps it was the prospect of a trip out of Kampala, Uganda, to the World Cup games in South Africa that put delegates to the International Criminal Court Review Conference in a magnanimous mood last June. Whatever the reason, years of acrimony and dissension melted into agreement. The consensus would have been remarkable even if the conference's agenda had been banal. In fact, it was not. At hand was the issue of the ICC's jurisdiction over the crime of aggression -- a subject so fraught that the delegates who originally negotiated the creation of the ICC in 1998 were only able to do so after deferring this issue until now, 12 years later.

The first noteworthy element of the conference was the presence of U.S. officials. The United States signed, but never ratified, the 1998 Rome Statute that created the court, and it has no vote in the ICC's Assembly of States Parties (ASP). Like other nonparties, though, it has always been eligible to attend meetings as an observer. But Washington has largely kept the ICC at arm's length since the Bush administration decided to withdraw the U.S. signature in May 2002, shortly before the court became operational. The administration feared that, once functional, the court would be a threat to U.S. sovereignty and put U.S. officials and military personnel at risk of prosecution in the course of their duties.

The Obama administration, which is generally more sympathetic to the ICC than its predecessor, took almost a year to review its policies toward the court before reengaging with it. The administration's first step was to send an observer to an ASP meeting in November 2009. Then, in a major address in March 2010, State Department Legal Adviser Harold Koh affirmed U.S. intentions to cooperate with the court. In June, Koh and Stephen Rapp, the ambassador-at-large for war crimes, led an observer delegation in Kampala of officials from a number of agencies and the military.

Much of the first week of the ICC conference was devoted to an assessment of the court's progress since it opened. The culmination was a declaration that included language welcoming the cooperation of nonparties in court proceedings. This pragmatic "welcome back" seemed an outgrowth of U.S. acknowledgement that the ICC is here to stay, as well as the court's recognition that, even though the United States will likely not join anytime soon, U.S. participation would be useful.

Then came the contentious issue of the crime of aggression. The idea of holding national leaders to account for waging wars of aggression has genuine moral appeal and historical pedigree. German and Japanese military leaders were prosecuted for aggression during the Nuremberg and Tokyo trials following World War II. But who defines the term and tries the cases is a thornier issue. Noting the absence of consensus on a definition of aggression in the run-up to the conference, U.S. officials questioned whether taking the matter up was not a bridge too far -- a foray into an area so contested that addressing it could undermine the court's other work.

The key question in Kampala was the relationship of the ICC to the United Nations Security Council. The UN Charter grants the Security Council "primary responsibility for the maintenance of international peace and security. If "primary responsibility" were translated into a requirement that the Security Council issue a finding of aggression before the ICC could act, the P-5 would be able to use their veto power to ensure that their nationals -- and their allies' nationals -- would never be at risk of prosecution. Such a situation would preserve the status quo, where might -- in the form of Security Council veto power -- makes right. If, on the other hand, the ICC asserted authority to operate independently on aggression, including an ability to prosecute nationals of nonparties, U.S. domestic politics would be so roiled as to doom the U.S. policy of practical cooperation.

In the end, the conference came to a consensus on a definition of aggression and on procedures for taking action, but only by providing adequate protections for the P-5. The ICC will not be able to bring aggression charges against a national of a state that is not a member of the ICC without a Security Council resolution under Chapter VII (responding to threats to peace and security). This protection is even stronger than that which governs the court's handling of other crimes; for example, the court could, in principle, charge a U.S. national for committing war crimes if he did so on the territory of a state party to the ICC. This is not the case for crimes of aggression.

If the ICC prosecutor wants to investigate a potential crime of aggression in the absence of a Security Council resolution, he first has to seek one. The Security Council has six months to take action before the prosecutor can investigate on his own authority. Finally, the Security Council retains the power to stop any investigation by voting annually to defer it.

States that belong to the ICC also have the option of individually opting out of the court's jurisdiction over aggression by filing a simple declaration. Proponents of expanding the reach of international law hope that, over time, opt-out states will be shamed into accepting ICC purview.

Finally, the Kampala outcome is subject to one further review. No sooner than January 1, 2017, the ASP will have to pass the aggression provisions by a two-thirds vote. The court then has jurisdiction effective one year after 30 members of the court ratify the amendments.

So fears that the ICC would be seeking to prosecute U.S. officials for aggression were overblown. For that to happen, the U.S. representative on the Security Council would have to either vote in favor of, or abstain from, a Security Council resolution asking the ICC to investigate the conduct of U.S. officials. Even if the United States eventually joins the court, it can choose to opt out of the court's jurisdiction over aggression.

At a June 15 briefing, Koh stated flatly, "The prosecutor cannot charge nationals of nonstate parties, including U.S. nationals, with a crime of aggression." He misspoke. The ICC's jurisdiction over aggression would not make sense without a Security Council trigger that could be pulled against any aggressor, whether a member of the ICC or not. However unlikely, it could be pulled against the United States; with a Security Council resolution, the prosecutor can investigate and bring charges against nationals of nonparties.

Indeed, the most likely scenario in which the ICC prosecutor might bring charges of aggression would be a Chapter VII resolution aimed at a situation beyond the reach of the ICC's other jurisdictional areas. Sudan, for example, is not a party to the ICC. Yet pursuant to a Security Council referral on Darfur, the ICC prosecutor has charged Sudanese President Omar Hassan al-Bashir with war crimes, crimes against humanity, and genocide. Next year, South Sudan will vote on secession, a vote widely expected to favor independence. Suppose Khartoum responds by sending troops to thwart that outcome. Were the court's new provisions on aggression already in effect, Bashir would be a prime candidate for a Security Council referral on charges of aggression.

Most of the states that are members of the ICC do not engage in activities that could even remotely be characterized as aggression. Their nationals are at no more legal risk of facing charges of aggression than they are for other crimes within ICC jurisdiction -- genocide, crimes against humanity, and war crimes. Some critics of the court have expressed concern that when the United States decides to take military action, it may find itself bereft of allies; members of the ICC might be reluctant to put their leaders at legal risk for aggression. This concern seems overstated. Members of the ICC have participated with the U.S. in combat operations in Iraq and Afghanistan, even though they could theoretically be prosecuted for other crimes within ICC jurisdiction.

For some countries, membership in the court and acceptance of its jurisdiction over aggression may have a little-discussed practical effect -- as an insurance policy against their own potential bad actors. Perhaps some would-be aggressors will be deterred from waging war because they would be eligible for prosecution at the ICC.

Whatever its eventual practical effects, what the ICC Review Conference in Kampala really tested was whether the aspirations of those in favor of strengthening the international legal regime could be squared with the concerns of the world's biggest power. The answer was yes.

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