World War I had a dramatic effect on nations and peoples throughout the world. In Europe, it led to the collapse of venerable empires and the emergence of several new nations based on the ambiguous principles of nationalism. In Asia, it spurred the rise of nationalist movements dedicated to freeing their societies from the ravages of Western colonialism. In Russia, it produced a cataclysmic revolution based on a new ideological paradigm that presented a mortal threat to the core principles of the Enlightenment. European rulers who had opted for war in 1914 to pursue their own dreams of national grandeur had reaped a whirlwind that would soon bring an end to a century of European domination over world affairs. Optimists had hoped that the bitter experience of a bloody conflict would usher in a new world “safe for democracy.” The reality was otherwise. The Great Depression of the 1930s undermined worldwide confidence in the capacity of the capitalist system to sustain modern progress even as it sowed the seeds of a second global conflict far more destructive than the first. It is to that devastating conflict that we must now turn.