The history of the atomic bomb is intertwined with the history of World War II, which itself grew out of the alliances and consequences of World War I. This conflict began in Europe in August 1914 and pitted the central powers—primarily Germany and Austria-Hungary—against the “Triple Entente” of Britain, France, and Russia. Expected to last a month, it quickly became bogged down in trench warfare that persisted for more than four years and killed 20 million people. The tide turned when the US entered the war on the side of the Triple Entente, forcing the central powers into submission. The subsequent peace treaty imposed severe economic penalties on Germany and also extracted some of its territory.

Germany transformed into the democratic Weimar Republic, but many Germans chafed at the humiliations of the Treaty of Versailles. Beginning in 1929, a massive, worldwide economic meltdown (the Great Depression) impoverished much of the US and Europe. Germans became sympathetic to a new movement, Adolf Hitler’s Nazi Party, which argued that the Jewish people had sold out the country during WWI and that its real destiny was to dominate Europe. Hitler won the top office of chancellor early in 1933, and within months he transformed the weakly democratic country into a dictatorship.