All law evolves in response to the context in which it is applied. In the past year, the global security context has changed dramatically. The primary threat no longer comes from States, but rather from non-State transnational actors, particularly terrorists. The sole remaining superpower’s response is a "global war on terrorism" that is neither a "war" in the classic sense, nor compatible with the rules of warfare designed for State-on-State hostilities. From the status of Guantanamo prisoners and the legality of CIA Predator strikes to questions about where the conflict may be conducted and when it will legally end, the jus in bello is proving ill-equipped to meet the new security challenges.

At the same time, possession, or the possibility thereof, of weapons of mass destruction have transformed otherwise insignificant States into global villains who dominate the world security agenda. In response, the United States issued a National Security Strategy that explicitly embraces pre-emptive strikes. It is a strategy, one supported by allies such as the United Kingdom, which is forcing the Security Council to become increasingly bellicose, lest it be left by the wayside.

Clearly, nascent security challenges are straining not only the jus in bello, but also traditional understandings of the jus ad bellum. What are we to make of this watershed year? As Bertrand Russell once observed, "Change is one thing, progress is another." The global security environment has changed and international law will surely evolve in parallel; whether that evolution is progress remains to be seen.

Michael Schmitt is professor of international law and director of the Executive Program in International and Security Affairs at the George C. Marshall European Center for Security Studies, in Garmisch-Partenkirchen, Germany.