The Soviet Union signed a non-aggression pact with Germany because it was forced to do so to ensure its security after the refusal of England and France to create an anti-German coalition together with the USSR. As recognised by authoritative, including Western historians, until mid-August 1939, right up to the failure of tripartite negotiations, Joseph Stalin aimed to create an anti-Hitler coalition within the USSR, France and Great Britain.
[Context: “A collection of archival documents was presented at the House of the Russian Historical Society in Moscow, proving that Hitler Germany was the initiator of the Molotov-Ribbentrop Pact.”] The Soviet Union was forced to sign this document in order to ensure its security.
A recurring disinformation narrative revising the Molotov-Ribbentrop Pact. This message is part of the Kremlin’s policy of historical revisionism and an attempt to portray Russia's role in World War II as non-aggressive. The Molotov-Ribbentrop Pact (the Treaty of Non-Aggression between Germany and the Union of Soviet Socialist Republics) was signed on August 23, 1939. Its secret protocols divided Europe into German and Soviet spheres of influence. Thus, the signing of the Molotov-Ribbentrop Pact directly caused the German and Soviet military aggression against Poland in September 1939, which resulted in complete occupation of the country by Germany and the USSR. The Treaty enabled the Soviet Union to invade and annex the Baltic States. The Soviets also annexed Romania's provinces of Bessarabia (today's Moldova) and northern Bukovina (now in Ukraine) and the Czechoslovak territory of Carpathian Ruthenia (now also part of Ukraine). Throughout the territories it occupied, the Soviet Union carried out harsh political reprisals, including mass executions and deportations. Also, the Soviet Union kept negotiating with Britain and France, but in the end, Stalin chose to reach an agreement with Germany. By doing so, he hoped to keep the USSR at peace with Germany and to gain time to build up the Soviet military establishment, which had been weakened by the purge of the Red Army officer corps in 1937. See another example referring to Molotov-Ribbentrop Pact here. Read more about the Molotov-Ribbentrop Pact: Molotov-Ribbentrop Pact: A 'honeymoon' for two dictators (Deutsche Welle); The Night Stalin and Hitler Redrew the Map of Europe (RFERL). Updated September 5, 2019: The headline of the summary of disinformation changed to reflect the original disinformation message.