By the end of 1941, the main lines of World War II had formed. Churchill referred to the "Grand Alliance" of the United Kingdom, the United States, and the Soviet Union, which together played the largest role in prosecuting the war. The alliance was largely one of convenience for each member: the U.K. realized that the Axis powers threatened not only its colonies in North Africa and Asia but also the homeland. The United States felt that the Japanese and German expansion should be contained, but ruled out force until Japan's attack. The Soviet Union, having been betrayed by the Axis attack in 1941, greatly despised German belligerence and the unchallenged Japanese expansion in the East, particularly considering their defeat in previous wars with Japan; the Soviets also recognized, as the U.S. and Britain had suggested, the advantages of a two-front war.