The school of realism in international relations suggests that all institutions are a function of the international power structure. Fundamental shifts in the latter rob the former of its foundation. From now on, realism advises us, we must accustom ourselves to more fragile and suboptimal forms of cross-border cooperation.

Multilateralism matters. As a growing number of issues become increasingly global, international cooperation is simply a must. Nonetheless, the multilateral system established at the end of World War II, with the founding of the United Nations and other organizations, is now unraveling in front of our eyes. This calls for a serious debate about why the system is unraveling, whether it can be saved, and what may replace it if not.

Multilateralism matters. As a growing number of issues become increasingly global, international cooperation is simply a must. Nonetheless, the multilateral system established at the end of World War II, with the founding of the United Nations and other organizations, is now unraveling in front of our eyes. This calls for a serious debate about why the system is unraveling, whether it can be saved, and what may replace it if not.

The school of realism in international relations suggests that all institutions are a function of the international power structure. Fundamental shifts in the latter rob the former of its foundation. From now on, realism advises us, we must accustom ourselves to more fragile and suboptimal forms of cross-border cooperation.

Multilateralism defined in its most rudimentary form—as the practice of three or more states coordinating policies—is not dead, of course. Short-term cooperation among groups of states has a long history and will continue to take place. However, the formation of complex multilateral regimes with persistent rules, followed by a wide range of governments to prescribe behavior and constrain state activity, is a much rarer phenomenon. Indeed, the multilateral system and institutions that emerged in the late 1940s are unique in human history. It is this system that is now falling apart.

The multilateralism index compiled by the International Peace Institute showed that the number of states and nongovernmental organizations signing up to the multilateral system continues to gro