At the Tehran Conference of the ‘Big Three’ (Stalin, Churchill and Roosevelt), Churchill proposed that the future Polish state should lie between the ‘Curzon Line’ and the ‘line of the Oder River, including within Poland East Prussia and Pomerania’. The official transcript does not record the American view. However, Roosevelt had a private meeting with Stalin during the proceedings (1 December 1943) at which he accepted the Soviet version of future Polish frontiers. In return, he asked for no publicity for this endorsement. As an additional precaution, he did not inform his own State Department of the arrangement. There were six or seven million US citizens of Polish origin, mainly Democrats, and he did not want to jeopardise their votes. He would seek an unprecedented fourth term in 1944. Polish-Americans were well organised and expected to hold the balance in key states such as New York, Illinois, Ohio and Pennsylvania. Stalin graciously concurred with these democratic niceties, noting that Soviet foreign policy did not suffer from such impediments. In fact, he was more than satisfied with their ‘secret agreement’. He asked US envoy Harriman to confirm it in June 1944 and received a ‘positive reply’.

In the same month, the Prime Minister of the Polish government in exile visited the USA. Mikołajczyk was assured that the USA was opposed to any agreements of frontier changes in Europe – or elsewhere – prior to the end of the war.