Summary:

Command & Conquer: Red Alert 3 is set in an alternate reality from World War II, in which the Western Allies fought the Soviet Union. In Red Alert 3 the Soviet leadership, facing defeat, goes back in time to kill Albert Einstein and prevent his assistance to the allies, paving the way for Soviet domination in the present. However, as an unintended consequence, a third world power, the Empire of the Rising Sun, is created and all three sides go to war.