On this date, August 23, 1939, Nazi Germany and the Soviet Union sign a non-aggression treaty, the Molotov–Ribbentrop Pact. In a secret addition to the pact, the Baltic states, Finland, Romania, and Poland are divided between the two nations.
The Molotov–Ribbentrop Pact, named after the Soviet foreign minister Vyacheslav Molotov and the Nazi German foreign minister Joachim von Ribbentrop, officially the Treaty of Non-aggression between Germany and the Union of Soviet Socialist Republics, and also known as the Ribbentrop–Molotov Pact or Nazi–Soviet Pact, was a non-aggression pact signed in Moscow in the late hours of 23 August 1939.
The pact's publicly stated intentions were a guarantee of non-belligerence by either party towards the other and a commitment that neither party would ally itself to or aid an enemy of the other party. This latter provision ensured that Germany would not support Japan in its undeclared war against the Soviet Union along the Manchurian-Mongolian border, ensuring that the Soviets won the Battles of Khalkhin Gol.
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 Nazi and Soviet "spheres of influence", anticipating potential "territorial and political rearrangements" of these countries. Thereafter, Germany invaded Poland on 1 September 1939. After the Soviet-Japanese ceasefire agreement took effect on 16 September, Stalin ordered his own invasion of Poland on 17 September. 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).
The pact remained in force until the German government broke it by invading the Soviet Union on 22 June 1941.
Of the territories of Poland annexed by the Soviet Union between 1939 and 1940, the region around Białystok and a minor part of Galicia east of the San river around Przemyśl were the only ones returned to the Polish state at the end of World War II. Of all other territories annexed by the USSR in 1939–40, the ones detached from Finland (Karelia, Petsamo), Estonia (Ingrian area and Petseri County) and Latvia (Abrene) remained part of the Russian Federation, the successor state of the Soviet Union, after 1991. Northern Bukovina, Southern Bessarabia and Hertza remain part of Ukraine.