On 26 May 1942 Britain and the Soviet Union signed a treaty. Though general in character, it was preceded by talks during which Britain to all purposes accepted the Soviet frontier adjustments that took place between September 1939 and June 1941. This meant that the incorporation of the Baltic states, Bessarabia and Bukovina, into Soviet territory was accepted as one of the war aims. The Polish frontier adjustments were included in these talks. Although their acceptance by Britain was not acknowledged, both Stalin and British politicians knew that, in the event of Poland being liberated by Soviet troops, Britain would not be able to reverse these earlier changes. British unwillingness to accept the frontier rectifications of September 1939 was the ostensible reason why both sides abandoned the text of the more detailed agreement discussed during the winter and spring of 1942. But the Soviet negotiators were left in no doubt that the Curzon Line would not be opposed by the British.

The thorny question of war aims and post-war territorial settlements had been introduced into British–Soviet talks by Stalin's letter to Churchill of 8 November 1941. In it the Soviet leader suggested that political talks had to precede any detailed agreements concerning joint strategy. Eden was forced to address himself to the issue in the full awareness that a failure to deal seriously with the Soviet request would heighten Soviet suspicions about British–American war objectives. He argued that the Soviet Union feared that the two Allies would ignore Soviet interests.