The USA entered World War Two against Germany and Japan in 1941, creating the Grand Alliance of the USA, Britain and the USSR.
This alliance brought together great powers that had fundamentally different views of the world, but who had to co-operate for four years against the threat from Germany and Japan.
The Grand Alliance would ultimately fail and break down, leading to the Cold War.
The alliance of the USA and the USSR brought together two sides that were divided by their political and economic ideologies.
However, the actions of Nazi Germany and its ally, Japan, in World War Two had brought political enemies together as the USA, USSR and Britain agreed to work to defeat fascism.