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The final collapse of the Soviet Union in 1991 brought a definitive end to the Cold War. It also brought an end to an international system defined by two superpowers and the beginning of a new global system defined by only one, the United States. The prevailing American ideology of international affairs—its literal worldview—had long been liberal internationalism, and the United States promptly proceeded to reshape global affairs according to its precepts. Now, two decades after its beginning, the global ascendancy of the United States and its ideology seems, to many observers, to be approaching its own end. It is an appropriate time, therefore, to review and reflect upon the course of liberal internationalism over the past two decades and, in particular, to discern what...