During the so-called Moscow Negotiations, which began in May and lasted until August 1939, the UK, France, Poland and the USSR could not find a compromise to create a coalition. Poland categorically refused to let the Red Army into its territory, fearing Soviet occupation. The USSR also started negotiations with Germany in parallel and on August 23, 1939, signed the Molotov-Ribbentrop (Stalin-Hitler) pact, in which the Soviet Union and Germany divided the spheres of interests in Europe: the division of Poland, the Baltic countries, Finland, and Romania were agreed.
On September 1 1939, Hitler attacked Poland, Soviet troops entered the territory on September 17 of the same year. From September 3 1939, Great Britain and France were at war with Germany, creating an anti-Hitler coalition together with the expelled Polish government and other countries.