The Western powers remained unaware of the top secret Nazi-Soviet Pact in 1939, which paved the way for World War II.
The German surrender in May 1945 was followed by a massive change in the political geography of Europe.
Poland's borders were redrawn by the Allies according to the demands made by Josef Stalin during the Tehran Conference, confirmed as not negotiable at the Yalta Conference of 1945.
The Polish government-in-exile was excluded from the negotiations.
The territory of Poland was reduced by approximately 20 percent.
Before the end of 1946 some 1.8 million Polish citizens were expelled and forcibly resettled within the new borders.
For the first time in its history Poland became a homogeneous one nation-state by force, with the national wealth reduced by 38 percent.
Poland's financial system had been destroyed.
Intelligentsia was largely obliterated along with the Jews, and the population reduced by about 33 percent.

Due to the territorial shift imposed from the outside, the number of Holocaust survivors from Poland remains the subject of deliberation.
According to official statistics, the number of Jews in the country changed dramatically in a very short time.
In January 1946, the Central Committee of Polish Jews (CKŻP) registered the first wave of some 86,000 survivors from the vicinity.
By the end of that summer, the number had risen to about 205,000–210,000 (with 240,000 registrations and over 30,000 duplicates).
The survivors included 180,000 Jews who arrived from the Soviet-controlled territories as a result repatriation agreements.
Another 30,000 Jews returned to Poland from the USSR after the Stalinist repressions ended a decade later.
The Western powers remained unaware of the top secret Nazi-Soviet Pact in 1939, which paved the way for World War II. The German surrender in May 1945 was followed by a massive change in the political geography of Europe. Poland's borders were redrawn by the Allies according to the demands made by Josef Stalin during the Tehran Conference, confirmed as not negotiable at the Yalta Conference of 1945. The Polish government-in-exile was excluded from the negotiations. The territory of Poland was reduced by approximately 20 percent. Before the end of 1946 some 1.8 million Polish citizens were expelled and forcibly resettled within the new borders. For the first time in its history Poland became a homogeneous one nation-state by force, with the national wealth reduced by 38 percent. Poland's financial system had been destroyed. Intelligentsia was largely obliterated along with the Jews, and the population reduced by about 33 percent.
Due to the territorial shift imposed from the outside, the number of Holocaust survivors from Poland remains the subject of deliberation. According to official statistics, the number of Jews in the country changed dramatically in a very short time. In January 1946, the Central Committee of Polish Jews (CKŻP) registered the first wave of some 86,000 survivors from the vicinity. By the end of that summer, the number had risen to about 205,000–210,000 (with 240,000 registrations and over 30,000 duplicates). The survivors included 180,000 Jews who arrived from the Soviet-controlled territories as a result repatriation agreements. Another 30,000 Jews returned to Poland from the USSR after the Stalinist repressions ended a decade later.
The Holocaust in Poland