Mahan had predicted back in the 1890s. As international trade doors slammed shut, large economies were forced to subsist largely on their own domestic produce. Domestic, in this context, included colonies, though, since one of empire’s chief benefits was the unrestricted economic access it brought to faraway lands. It mattered to major imperial powers—the Dutch, the French, the British—that they could still get tropical products such as rubber from their colonies in Asia. And it mattered to the industrial countries without large empires—Germany, Italy, Japan—that they couldn’t.
