The agreement between the British Prime Minister, Neville Chamberlain, and Adolf Hitler at Munich in September 1938, which led to the German invasion of Czechoslovakia, was arrived at without the participation of the Soviet Union, and led Stalin to conclude that Britain and France were leaving Germany a free hand against the USSR. Whether Stalin was right to draw this conclusion is a question that need not detain us; suffice it to say that he was wrong, because Hitler's intention was to attack first in the west. Nevertheless, Stalin, who had been involved in secret negotiations with Hitler since 1936, was convinced that Chamberlain, supported by the French government, was encouraging Germany to turn eastwards. Two days after the collapse of military talks between the USSR, France and Great Britain, Stalin and Hitler signed the Nazi–Soviet pact on 23 August 1939.

The signing of the pact demanded an intellectual leap on the part of the world communist movement, from one of outright opposition to fascism to one of open opposition to Western imperialism. On 24 August Moscow Centre withdrew its secret agents from Germany, and severed radio links with German nationals working for Soviet intelligence inside the Third Reich. The following day the German Communist Party issued a statement calling on communists to ‘support the peace policy of the Soviet Union’:

On 7 September Stalin told the Bulgarian communist Georgi Dimitrov, general secretary of the Comintern, what he expected of foreign Communist parties. ‘They should denounce their governments’ war plans as imperialistic and reduce anti-Fascist propaganda.’ On the eleventh, with the war barely a week old, the Communist Party of the United States declared the war to be a conflict between ‘imperialist’ nations. On the 14th a broadcast from Soviet Russia announced that the war was an ‘imperialist’ one, and a ‘predatory’ conflict pursued by two aggressor nations.