While the Nazis and the Japanese built their empires, Great Britain (the greatest colonial power), the United States (the greatest capitalist power), and the Soviet Union (the greatest Communist power) joined together in an unlikely military pact called the Grand Alliance. The vagaries of war, rather than choice, brought them together. Stalin had been cooperating with Hitler before Germany attacked Russia in June 1941, and the United States entered the war only after the Japanese attack on Pearl Harbor in December.

Grand Alliance leaders Stalin and Roosevelt agreed to a Europe first policy as proposed by Winston Churchill (Chamberlain’s successor as British prime minister). 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 (as Russia had signed with Germany in World War I). 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, which it harnessed in 1943 to out produce not only the Axis powers but also the rest of the world combined.30 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 strength that it might well have defeated Germany without Western help. In the face of the German advance, whole factories and populations were successfully evacuated to eastern Russia and Siberia. There war production was reorganized and expanded, and the Red Army was increasingly well supplied and well led. Above all, Stalin drew on the massive support of the people for what the Soviets called the “Great Patriotic War of the Fatherland.”