This is a pro-Kremlin conspiracy narrative about WWII and the Munich Agreement.
The Munich Agreement (signed 30 September 1938), did indeed permit German annexation of the Sudetenland, in western Czechoslovakia. The policy of appeasement towards Adolf Hitler was heavily criticised in Europe and proved to be a disastrous move. But World War II began in Europe on September 1 1939, after the signature of the Molotov-Ribbentrop pact, when Hitler attacked Poland. Soviet troops entered the territory on September 17 of the same year. Great Britain and France responded by declaring war on Germany on 3 September, creating an anti-Hitler coalition together with the expelled Polish government and other countries.
Before this, from May 1939 until August 1939, the UK, France, Poland and the USSR were trying to find a compromise to create a coalition during the so-called Moscow Negotiations. Poland categorically refused to let the Red Army into its territory, fearing Soviet occupation. The USSR started in parallel negotiations with Germany and on 23 August 1939, signed the Molotov-Ribbentrop (Stalin-Hitler) pact, in which the Soviet Union and Germany divided their "spheres of interests" in Europe: the division of Poland, the Baltic countries, Finland, and Romania were agreed.
Read a similar case that The Munich conspiracy of European powers launched WWII.