While the Nazis and the Japanese built their empires, Great Britain, the United States, and the Soviet Union joined together in an unlikely military pact called the Grand Alliance. Grand Alliance leaders agreed to a Europe first policy. Only after defeating Hitler would the Allies mount an all-out attack on Japan. To encourage mutual trust, the Allies adopted the principle of the unconditional surrender of Germany and Japan, and no unilateral treaties. This policy cemented the Grand Alliance because it denied Germany and Japan any hope of dividing their foes.

The Grand Alliance’s military resources were awesome. The United States possessed a unique capacity to wage global war with its large population and mighty industry. The British economy was totally and effectively mobilized, and the country became an important staging area for the war in Europe. As for the Soviet Union, so great was its economic strength that it might well have defeated Germany without Western help.