Imagine that you were alive in the summer of 1900, living in London, then the capital of the world. Europe ruled the Eastern Hemisphere. There was hardly a place that, if not ruled directly, was not indirectly controlled from a European capital. Europe was at peace and enjoying unprecedented prosperity. Indeed, European interdependence due to trade and investment was so great that serious people were claiming that war had become impossible—and if not impossible, would end within weeks of beginning—because global financial markets couldn’t withstand the strain. The future seemed fixed: a peaceful, prosperous Europe would rule the world.

Imagine yourself now in the summer of 1920.