All great powers have a deeply ingrained self-perception shaped by historical experience, geography, culture, beliefs, and myths. Many Chinese today yearn to recover the greatness of a time when they ruled unchallenged at the pinnacle of their civilization, before “the century of humiliation.” Russians are nostalgic for Soviet days, when they were the other superpower and ruled from Poland to Vladivostok. Henry Kissinger once observed that Iranian leaders had to choose whether they wanted to be “a nation or a cause,” but great powers and aspiring great powers often see themselves as both. Their self-perception shapes their definition of the national interest, of what constitutes genuine security and the actions and resources necessary to achieve it. Often, it is these self-perceptions that drive nations, empires, and city-states forward. And sometimes to their ruin. Much of the drama of the past century resulted from great powers whose aspirations exceeded their capacity.