The First World War brings an end to most imperial regimes, but on the eve of World War II, the British Commonwealth of Nations continues to stretch from North America to Southwest Asia, encompassing nearly one-quarter of the world population. By 1938, two decades have passed since a generation of young British men were lost in the trenches of France and Belgium, and there remains little public appetite for another such conflict. When Hitler, backed by a rebuilt German military, threatens to reclaim the Sudetenland—a portion of Czechoslovakia that includes three million ethnic Germans—the British pin their hopes on diplomacy to defuse tensions.