The Molotov-Ribbentrop Pact, otherwise known as the Nazi-Soviet Pact, was signed by Vyacheslav Molotov (Stalin's Soviet foreign minister) and Joachim von Ribbentrop (Hitler's German foreign minister) on 23 August 1939. The pact promised that neither the Soviet Union nor Nazi Germany would attack each other. A secret part established spheres of interest, which later became a border between both countries when they later invaded and divided Poland.
More than a week later, 1 September 1939, the German invasion of Poland began. 16 days after that, the Soviet invasion of Poland began, 17 September.
About 250,000 to 454,700 Polish soldiers and policemen were captured and interned by the Soviet authorities. 125,000 were imprisoned in camps run by the NKVD. About 43,000 soldiers born in western Poland, then under German control, were transferred to the Germans. In turn, the Soviets received 13,575 Polish prisoners from the Germans. This showed close co-operation between the Nazis and the Soviets.
On 3 September, France and the United Kingdom declared war soon because both countries had promised to defend Poland if it was attacked. Neither country was ready for war and so for some time, nothing could be done to help Poland, but World War II had clearly started on that day.
- Fisher, David & Read, Anthony 1999. The Deadly Embrace: Hitler, Stalin, and the Nazi–Soviet Pact 1939–1941. New York: W.W. Norton & Co.
- Garlinski, Jozef 1987. Poland in the Second World War. Hippocrene Books. ISBN 0-333-39258-2
- Taylor AJP 1961. The Origins of the Second World War. London: Simon & Schuster. ISBN 978-0-684-82947-0