America, England, and Russia teaming up to destroy Hitler's Germany.
Germany invaded Poland in September 1939, which caused Britain and France to declare war. Germany then invaded Russia in June 1941, which resulted in a two-front war. The U.S. was attacked by Germany's ally, Japan, in December 1941, which drew the U.S. into war against both Japan and Germany.
In all cases, the first strike was committed by Axis countries against the Allies.