In 1936, Germany and Japan signed the Anti-Comintern Pact, which was a pact against the growth of communism, and therefore essentially against Russia herself. Stalin tried to make an alliance with Britain and France in order to try and protect Russia, however both declined, and instead Stalin had to try and negotiate a treaty with Germany. In August 1939, Ribbentrop and Molotov, the Foreign Ministers for Russia and Germany respectively, signed the Molotov-Ribbentrop Pact, which agreed that neither country would invade the other, whilst at the same time split Eastern Europe up between the two powers.
However, Hitler viewed the Slavic people of Russia as sub-human, much like the Jews. His troops were given the freedom to kill Soviets or enslave them for the nazi war effort. On top of this, Hitler required Lebensraum, and always assumed it would come from the east. From Russia. The USSR had a vast amount of natural resources and raw materials that Hitler also wanted, which gave him added motivation to go through with an invasion.
On the 22nd June 1941, Operation Barbarossa was implemented, and the USSR was invaded by Germany. Unprepared, with Stalin ignoring his intelligence service and not preparing his Red Army, the German army was split into three groups whose objectives were to attack Leningrad, Kiev and Moscow, and the Black Sea area and Stalingrad using the Blitzkrieg tactic. By the end of September, German forces had reached Leningrad, but weren't able to make further progress, so instead changed tactic and sieged the city - for three years. By December, German forces had reached Moscow, however due to Operation Barbarossa being held back for five weeks, the winter set in and the German advance stalled as they were ill prepared with few items of winter clothing, and weapons that became useless as the fuel within them froze. The Germans were forced to retreat.
By the end of 1941, the German army controlled a huge area of Russia, and 45% of the total population. The USSR was cut off from the grain supplies of the Ukraine as well as areas rich in coal and steel. Hundreds of thousands of Soviet soldiers were killed, wounded or taken prisoner, as well as the country suffering massive losses of tanks, aircraft and artillery.
However, after disappearing…