Europe 1940: Winter War
On 17 September 1939 the Soviet Union moved to occupy eastern Poland as had been agreed with Germany. The Soviets followed this by establishing influence over the Baltic states and attempting to invade Finland. Finnish defences were unexpectedly tough, however, and the Russians were forced to make do with territorial concessions.
17 Sep–6 Oct 1939 Soviet Invasion of Poland▲
In accordance with the Molotov-Ribbentrop Pact, the Soviet Union invaded Poland on 17 September, meeting the Germans invading from the west on 6 October. On 1 November, the Soviets annexed Eastern Poland, incorporating its territory into the Belarusian and Ukrainian Soviet Socialist Republics.
29 Sep–10 Oct 1939 Soviets establish influence over Baltic states▲
The Soviet Union demanded the establishment of bases in Estonia, Latvia, and Lithuania. In exchange, the Soviet Union ceded the historically disputed city of Vilnius to Lithuania from what had been Poland.
30 Nov 1939–13 Mar 1940 Winter War▲
The Soviet Union invaded Finland with some 450,000 men, without declaring war and in violation of three non-aggression pacts. Despite numerical superiority, the Soviets suffered repeated setbacks until reinforcements allowed them to break through in January 1940. At the Moscow Peace Treaty, the Finns agreed to cede significant territory along the border of the two states, including the Karelian Isthmus.