The Polish transfers were among the largest of several post-war expulsions in Central and Eastern Europe, which displaced a total of about 20 million people.
According to official data, during the state-controlled expulsion between 1945 and 1946, roughly 1,167,000 Poles left the westernmost republics of the Soviet Union, less than 50% of those who registered for population transfer.
Many of the deported Poles were settled in historical eastern Germany; after 1945, these were referred to as the "Recovered Territories" of the Polish People's Republic.
More Poles migrated to this area after the Union of Lublin in 1569, when most of the territory became part of the newly established Polish–Lithuanian Commonwealth.
Social and ethnic conflicts arose regarding the differences in religious practices between the Roman Catholic and the Eastern Orthodox adherents during the Union of Brest in 1595-96, when the Metropolitan of Kyiv-Halych broke relations with the Eastern Orthodox Church and accepted the authority of the Roman Catholic Pope and Vatican.
[13] The partitions of Poland, toward the end of the 18th century, resulted in the expulsions of ethnic Poles from their homes in the east for the first time in the history of the nation.
Throughout the existence of UNR (1917–21), there was a separate ministry for Polish affairs, headed by Mieczysław Mickiewicz; it was set up by the Ukrainian side in November 1917.
Beginning in 1920, the Bolshevik and nationalist terror campaigns of the new war triggered the flight of Poles and Jews from Soviet Russia to newly sovereign Poland.
[21]: 7 In the autumn of 1935, Stalin ordered a new wave of mass deportations of Poles from the western republics of the Soviet Union.
Poles were expelled from the border regions to resettle the area with ethnic Russians and Ukrainians, but Stalin had them deported to the far reaches of Siberia and Central Asia.
In the following few years in Kresy, the lands assigned to sovereign Poland, some 8,265 Polish farmers were resettled with help from the government.
On 12 July 1930, activists of the Organization of Ukrainian Nationalists (OUN), helped by the UVO, began the so-called sabotage action, during which Polish estates were burned, and roads, rail lines and telephone connections were destroyed.
[27] OUN directed its violence not only against the Poles but also against Jews and other Ukrainians who wished for a peaceful resolution to the Polish–Ukrainian conflict.
Spreading terror throughout the region, the Soviet secret police (NKVD) accompanying the Red Army murdered Polish prisoners of war.
[30][31] From 1939 to 1941 the Soviets also forcibly deported specific social groups deemed "untrustworthy" to forced labor facilities in Kazakhstan and Siberia.
Nikita Khrushchev, however, approached Stalin personally to keep the territories gained through the illegal and secret Molotov–Ribbentrop pact under continued Soviet occupation.
The document specified who was eligible for the resettlement (it primarily applied to all Poles and Jews who were citizens of the Second Polish Republic before 17 September 1939, and their families), what property they could take with them, and what aid they would receive from the corresponding governments.
The Polish underground press in Lviv characterized these acts as attempts to hasten the deportation of Poles from their city.
Local Polish clergy were active in agitating against leaving, and the underground press called those who had registered for repatriation traitors.
Many ethnic Poles hoped that a post-war Peace Conference would assign the Vilnius region to Poland.
The Lithuanian communist party was dominated by a nationalist faction [citation needed] which supported the removal of the Polish intelligentsia, particularly from the highly contested Vilnius region.
[39] The city of Vilnius was considered a historical capital of Lithuania; however, in the early 20th century its population was around 40% Polish, 30% Jewish and 20% Russian and Belarusian, with only about 2–3% self-declared Lithuanians.
[citation needed] The government considered the rural Polish population important to the agricultural economy, and believed those people would be relatively amenable to assimilation policies (Lithuanization).
The rural population was denied the right to leave Lithuania, due to their lack of official pre-war documentation showing Polish citizenship.
[1]: 141 [39] Contrary to the government's agreement with Poland, many individuals were threatened with either arrest or having to settle outstanding debts if they chose repatriation.