The Molotov-Ribbentop pact, sometimes called the Hitler-Stalin pact, was a non-aggression treaty between Nazi-Germany and the Soviet Union. It was signed in Moscow on August 23, 1939 by the foreign ministers Vyacheslav Molotov and Joachim von Ribbentrop.
The European balance of power established at the end of World War I eroded step by step from the Abyssinia crisis[?] (1935) to the Munich Agreement (1938). The dissolution of Czechoslovakia was the beginning of a new political development, where Germany and the Soviet Union aspired to regain territories and provinces lost in the aftermath of World War I. Hence the Soviet Union was not interested in maintaining the status quo, but rather in encouraging the conflict between capitalist countries - also in order to enhance the spread of the revolution.
Negotiations between the Soviet Union and France/Britain for a military alliance against Germany stalled, mainly due to mutual suspicions. The Soviet Union sought guarantees for support against German aggression beside recognition of Soviet commitment to interfer against "a change of policy favorable to an aggressor" in the countries along the western Soviet border, which the Soviet Union preferred to express as "Soviet guarantees for the independence of Finland, Estonia, Latvia, Poland, Rumania, Turkey and Greece", regardless of if those countries wanted such guarantees, or not.
Instead Stalin opened for negotiations with Nazi-Germany by replacing the Jewish Foreign Minister Maxim Litvinov[?] by Molotov, and the negotiations could then soon be successfully concluded.
The pact was announced as a non-aggression pact, but in a secret appendix Eastern Europe was divided between Germany and the Soviet Union. Bessarabia, Finland, Estonia and Latvia was Soviet's agreed share. The rivers Narev[?], Vistula and San were agreed on as a new suitable border between Germany and the Soviet Union, and a week after the pact was signed in Moscow, the partition of Poland was commenced with Germany's attack on September 1st followed by the Soviet Union on September 17th (see also: Partitions of Poland).
September 28th 1939 the three Baltic Republics were given no choise but to sign a so called Pact of defense and mutual assistance, which permitted the Soviet Union to station troops in Estonia, Latvia and Lithuania.
Finland was less humble and had on November 30th 1939 to suffer an attempted invasion, which however was resisted in the Winter War. After over three months of hard fights and heavy losses the Soviet Union confined with 10% of Finland's territory.
In June 1940, after Germany's swift victories and occupation of Norway, Denmark, the Netherlands, Belgium and France it was time for Bessarabia and the three Baltic states to suffer occupation, and soon annexion, to the Soviet Union. Thereby the Molotov-Ribbentrop pact was exhausted, as Germany opposed further assaults against Finland (see: the Continuation War).
A famous cartoon by David Low from the London Evening Standard of 20 September 1939 has Hitler and Stalin bowing to each other over a corpse, with Hitler saying "The scum of the Earth, I believe?" and Stalin saying "The bloody assassin of the workers, I presume?". The pact had been a particular shock to supporters of communism in the West.