Command & Conquer: Red Alert takes place between 1946 and 1953 of a parallel universe.
Starting out at the Trinity Site in New Mexico in 1946 (in our timeline), Albert Einstein prepares to travel backward in spacetime. He activates his experimental time machine to find himself in Landsberg, Germany, on 20 December 1924, where he meets a young Adolf Hitler just after the latter's release from Landsberg Prison. Following a brief conversation between the two, Einstein shakes Hitler's hand while activating his time-traveling device. In the process of Einstein returning to his time of origin, Hitler dies due to the lack of his own equipment for the transit through time. (This is implied by the Allies' Chronosphere in-game, in which usage of its power on soldiers kills them.)
Hitler's death prevents him from rising to power as leader of Nazi Germany. This creates a new timeline, in which eliminating Hitler's actions has caused a change for the worse. Without Nazi Germany, the Soviet Union grew powerful under the rule of Joseph Stalin. Unweakened, the USSR seizes land from China and then invades Eastern Europe, to achieve Joseph Stalin's vision of a Soviet Union stretching across the entire Eurasian landmass. In response, the nations of Europe form the Alliance, and start a guerrilla war against the invading Soviet army. Over the course of the game's story, the Allies and Soviets fight for control over the European mainland in an alternate World War II.
Red Alert was praised for its user interface, which claimed to be more developed than the competing games of its time. Players could queue commands, create unit groups that could be selected by a number key, and control numerous units at a time. The game was known to be easy to control, simple to learn and responsive to users' commands. It also featured two factions that had differing styles of play.