From Wikipedia:
The Molotov–Ribbentrop Pact, colloquially named after the Soviet foreign minister Vyacheslav Molotov and the German foreign minister Joachim von Ribbentrop, was an agreement officially titled the Treaty of Non-Aggression between the Third German Reich and the Union of Soviet Socialist Republics and signed in Moscow in the early hours of 24 August 1939 (but dated 23 August). n addition to stipulations of non-aggression, the treaty included a secret protocol dividing Northern and Eastern Europe into German and Soviet spheres of influence, anticipating potential "territorial and political rearrangements" of these countries. Thereafter, Germany and the Soviet Union invaded their respective sides of Poland, dividing the country between them. Part of eastern Finland was annexed by the Soviet Union after an attempted invasion. This was followed by Soviet annexations of Estonia, Latvia, Lithuania and eastern and northern Romania. The protocol is considered a crime against peace as a conspiracy to conduct war of aggression.