That was the beginning of a conflict between the two totalitarian states.

Earlier, on 23 August 1939, the German Reich and the Soviet Union jointly planned and proceeded to divide among themselves the territories of free states: Poland, Finland, Lithuania, Latvia, Estonia and part of Romania. On 1 September 1939, Germany invaded Poland from the west, north and south (with the support of Slovakia). On 17 September 1939, the Soviet Union, honouring all its commitments towards Hitler, attacked Poland from the east. In this way, both countries jointly started World War II. In line with the secret protocol of the Molotov-Ribbentrop Pact, the Soviets attacked Finland, and in 1940, annexed Lithuania, Latvia and Estonia, as well as Romanian Bessarabia and Bukovina. Abundantly supplied with Soviet natural resources and raw materials, Hitler conquered Denmark, Norway, Belgium, the Netherlands and Luxembourg. With Soviet economic support, he defeated France and launched an invasion of Great Britain. In 1941, he attacked Yugoslavia and Greece.

In the conquered lands, both countries unleashed the reign of terror against enslaved communities. They committed genocide of civilians, followed by mass deportations.

Ruling almost the entire continent, on 22 June 1941, the Germans attacked the Soviet Union. The former allies started a war against each other. It was a conflict between two criminal totalitarian states.

Despite the fact that the Soviet Union became one of the Allied powers in 1941, it did not change its totalitarian face. Following a series of defeats, in 1943 the Soviets took the initiative on the eastern front. Instead of bringing freedom to the nations conquered by the Germans, as the Allies pledged, the USSR took advantage of its victories to enslave Central and Eastern Europe. Poland, one of the Allies that fought against the German Reich throughout the whole war, became one of the countries dominated by the Soviet totalitarian regime in the years 1944-1945.