Recurring pro-Kremlin disinformation narrative distorting the events of the Second World War.
By signing the non-aggression pact with Nazi Germany in August 1939, the Soviet Union became complicit in the breakout of WWII. Following the conclusion of the agreement, the two dictatorships would remain allies for the next 22 months. The deal was accompanied by a secret supplementary protocol on the delimitation of areas of mutual interest in Eastern Europe. In particular, Hitler and Stalin agreed to divide Poland. The agreement also indicated that the Baltic states of Latvia, Estonia and Lithuania, as well as Bessarabia and Finland, also belonged to the respective areas of interest of Germany and the USSR.
A mere week after the pact's signing, Germany attacked Poland and started World War II. On 17 September, Soviet troops invaded Polish territory from the east.
See here for expert commentary on Soviet/Russian myth-making around WWII, including efforts to diminish the geopolitical role and scope of the Nazi-Soviet pact.