From the game's rule book:
"At 3:15 AM on June 22, 1941, the German army launched the invasion of the Soviet Union, code named Operation Barbarossa. For the next three months, the blitzkreig carried the Germans deep into Russia, wreaking enormous destruction upon the Red Army. Then the Russian winter intervened, and after a last-gasp offensive that reached the very gates of Moscow, the Germans were thrown back. By April of 1942, after nine months of desperate warfare, six million men and women lay dead. But in May the germans mounted a second offensive -- and by March of 1943 the death toll had doubled, while Russia was stronger than ever. This was Gotterdammerung: the death of Titans. Eastern Front (1941) recreates Operation Barbarossa."