The end of the Cold War ushered in a unipolar world, cementing U.S. dominance over a generally liberal international order. Yet where once it seemed that U.S. foreign policy would be simpler and easier to manage as a result, the events of the past 15 years—the 9/11 attacks, the invasions of Afghanistan and Iraq, the Arab Spring, and Russia’s invasions of Georgia and Ukraine—strongly suggest otherwise. The world today is certainly safer for Americans than it was under the existential threat posed by the Soviet Union. But the world is undoubtedly more complex, as nonstate actors, shifting alliances, and diverse domestic political factors complicate U.S. foreign policy formation and implementation. A robust debate on America’s foreign policy choices is urgently needed...