Soviet Union in World War II

The Soviet Union signed a non-aggression pact with Nazi Germany on 23 August 1939. In addition to stipulations of non-aggression, the treaty included a secret protocol that divided territories of Romania, Poland, Lithuania, Latvia, Estonia and Finland into German and Soviet "spheres of influence", anticipating potential "territorial and political rearrangements" of these countries. Stalin and Hitler later traded proposals after a Soviet entry into the Axis Pact.

Germany invaded Poland on 1 September 1939. Joseph Stalin waited until 17 September before launching his own invasion of Poland. Part of southeastern (Karelia) and Salla region in Finland were annexed by the Soviet Union after the Winter War. This was followed by Soviet annexations of Estonia, Latvia, Lithuania, and parts of Romania (Bessarabia, Northern Bukovina and the Hertza region). It was only in 1989 that the Soviet Union admitted the existence of the secret protocol of the Nazi-Soviet pact regarding the planned divisions of these territories. The invasion of Bukovina violated the Molotov-Ribbentrop Pact, as it went beyond the Soviet sphere agreed with the Axis.

In 1940-41 Stalin ignored reports of an Axis invasion. On 22 June 1941, Hitler launched an invasion of the Soviet Union. Stalin was confident that the total Allied war machine would eventually stop Germany, and with Lend Lease from the West, the Soviets stopped the Wehrmacht some 30 kilometres from Moscow. Over the next four years, the Soviet Union repulsed Axis offensives, such as at the Battle of Stalingrad and Battle of Kursk, and pressed forward to victory in large Soviet offensives such as the Vistula-Oder Offensive. Stalin began to listen to his generals more after Kursk.

...
Wikipedia