The Grand Alliance, also known as The Big Three, was a military alliance consisting of the three major Allies of World War II: the Soviet Union, the United States, and the United Kingdom. It is often called the "Strange Alliance" because it united the world's greatest capitalist state, the greatest communist state and the greatest colonial power.

The Grand Alliance was one of convenience in the fight against the Axis powers. The British had reason to ask for one as Germany, Italy, and Imperial Japan threatened not only the colonies of the British Empire in North Africa and Asia, but also the United Kingdom. The United States felt that the Japanese and German expansion should be contained, but ruled out force until the attack by the Imperial Japanese Navy on Pearl Harbor on 7 December 1941.

The Soviet Union, after the breaking of the Nazi–Soviet Pact by the instigation of Operation Barbarossa in 1941, greatly despised the unchallenged Japanese expansion in the East, particularly considering their defeat in several previous wars with Japan. They also recognized, as the US and Britain had suggested, the advantages of a two-front war. In 1942 the three powers discussed becoming, with China, the Four Policemen of world peace.

More Info: