The source of these conflicts was Poland’s eastern territory, which the Soviet Union long had aspirations for and gained through armed aggression in September 1939. Similarly to how the French did not wish to die in 1939 for Gdansk, so too did the British not wish to fight for Vilnius and Lviv. The rifts intensified in 1941 when Moscow became an ally of London and then subsequently Washington, and the Red Army became the only force fighting Hitler in Europe. To placate and satisfy Stalin, first Churchill and then Roosevelt were capable of not only ceding Poland’s eastern territory but placing all of Poland under Soviet domination.
First General Sikorski was forced to sign a pact with Stalin (See Katyn..) in which the question of national boundaries was totally omitted. The worsening relations between the Soviet Union and the Polish Government in exile also had a cooling effect on the latter’s relations with Western allies. Moscow’s decision to sever relations with the Polish government in exile in April 1943 actually suited Churchill, who could now communicate with Stalin directly over the heads of the London Poles, especially after the July 4 1943 airplane disaster in which General Sikorski, who commanded great authority among the Allies, perished. His successor, Stanislaw Mikolajczyk, did not inherit such a strong standing.
Churchill and Roosevelt’s agreement to concede Poland’s eastern territory, but Poland was too be compensated with Germany territory, thereby moving the country from the East to the West. This decision was made during the Tehran Conference (28 November – 1 December 1943) without informing the Polish government in exile or seeking their permission. Polish protests had no chance of success, as Stalin held an ever stronger deck of cards: the failure of Operation Tempest, the installation of a pro-Soviet Polish government to the West of the Bug River, and the pacification of the Warsaw Uprising. Stalin could now not only demand Poland’s eastern territory, but also make Poland into a vassal.
On January 12, 1945, a great Soviet offensive was launched, which in a matter of three weeks reached the Oder River. This served as a convenient backdrop to the Yalta Conference which began on February 3. The focus was not so much on Poland’s boundaries, as to the makeup of its future government. At the conference it was decided to expand the communist domination Provisional Government of the Republic of Poland to include “Democratic activists” from Poland and abroad. The new cabinet was to be recognized by the allies and carryout free elections. Talks to form a Provisional Government of National Unity were held in Moscow in June 1945. At the same time in the Soviet capital, a show trial was being held of the Polish Underground Leadership (The Trial of 16) which was to be a tool of political pressure. It proved effective, the government was established and the Western Allies revoked their recognition of the Polish government in exile. The Potsdam Conference (July 17-August 2 1945) only confirmed the current state of affairs, and solidified the map of not only Europe, but of the world for the next half century.