The three great powers, Britain, the United States and the U.R.S.S., the main supporters of the war against the Axis forces, differed greatly in their interests, ideology and system of government. The Anglo-Soviet Mutual Aid Agreement (July 1941) and especially the Atlantic Charter (August 1941), by which England and the U.S.A. they declared their common political goals, hastened the official conclusion by the United Nations Declaration (January 1, 1942, Washington) signed by 26 states that pledged to cooperate and not to conclude separate peace with the aggressor.

This alliance was wartime, as its members realized, not based on trust but on necessity; it was not a "deep feeling of common values ​​or similar interests, but only opposition to a single enemy." The need for synchronization during the war and post-war goals will often test the alliance. Naturally, the Three Great Ones will try to avoid the fragile alliance disintegration, as much as possible, in order to be able to fulfill the purposes for which they entered the war: the defeat of the Axis, the establishment of new principles of international order, peaceful coexistence, etc.