The Axis and Allies
Who fought alongside whom, and how alliances changed
1939–1945
The Axis and Allies were the two principal coalitions of the Second World War. Germany, Italy and Japan formed the core of the Axis. Britain, the Soviet Union, the United States and China were key Allied powers. Membership, relationships and enemies changed during the war; these were not two fixed groups present in their final form from the beginning.
How the Axis took shape
Nazi Germany, Fascist Italy and Japan pursued their own expansionist goals. The September 1940 Tripartite Pact formally united them as the Axis. The alliance connected European and Asian conflicts, but each state retained its own leadership and decisions. Mussolini’s Italy, for example, entered the war against Britain and France in June 1940; Japanese attacks on the United States came in December 1941.
The Allies were not the same from the start
Britain and France declared war on Germany after its invasion of Poland in September 1939. China was already fighting Japan. The Soviet Union initially had a non-aggression agreement with Germany and itself invaded eastern Poland. Germany’s invasion in June 1941 then put it on the other side of the fighting.
The United States supplied Germany’s and Japan’s opponents before entering the war. After Pearl Harbor, it declared war on Japan; Germany and Italy then declared war on the US. At the beginning of 1942, Britain, the Soviet Union, the United States and China joined other governments in pledging not to make a separate peace.
A common enemy, different states
Allied cooperation did not erase differences between democracies and Stalin’s dictatorship, or between imperial powers and people under their rule. Nor did it mean every member fought every Axis state: the Soviet Union remained neutral towards Japan until August 1945.
Military needs required joint planning. At Casablanca in 1943, Roosevelt and Churchill discussed the Mediterranean, a future front in France, aid to the Soviet Union and war against Japan. Allied strategy combined a shared goal with different priorities.
Why cooperation mattered
The Allies combined armies, industry, labour and transport across distant regions. Lend-Lease moved American war supplies to other fighting states. Economic and population resources became increasingly important in a prolonged war. After victory, disputes over postwar security and political power progressively undermined the wartime alliance.
Explore further
- Allied strategy
How a shared goal translated into choices of fronts and supplies.
- The 1939 pact
Germany’s relationship with the Soviet Union before their war.
- Japanese expansion
Asia’s road into the global conflict.