The popularity of alternative approaches to international politics cannot be explained entirely by their scholarly virtues. Among the other factors at work are fashions and normative and political preferences. This in part explains the increasing role of rationalism and constructivism. Important as they are, these approaches are necessarily less complete than liberalism, Marxism, and realism. Indeed, they fit better with the latter than is often realized. Realism, then, continues to play a major role in IR scholarship. It can elucidate the conditions and strategies that are conducive to cooperation and can account for significant international change, including a greatly decreased tolerance for force among developed countries, which appears to be currently the case. But neither it nor other approaches have as yet proved to be reliable guides to this new world.