The first spontaneous flight of about 500,000 Poles occurred during the reconstitution of sovereign Poland following World War I. In the second wave, between November 1919 and June 1924, roughly 1,200,000 people left the territory of the USSR for Poland amid political repression of Polish–Soviet War and its aftermath. It is estimated that some 460,000 of them spoke Polish as a first language. However, throughout the interwar years, according to Polish estimates, some 1,2 million up to 1,3 million Poles remained in the vast territories of the Soviet Union including 260,000 in the former Minsk Voivodeship (Mińszczyzna), 230,000 in the Gomel Region (Homelszczyzna), 160,000 in the Kyiv region (Kijowszczyzna), and 300,000 in Podole region with roughly the same number spread out across the rest of the country. None of them were allowed to leave. In 1937–38 Polish minority became the target of the Polish Operation of the NKVD, in which 111,091 ethnic Poles were killed. The number of ethnic Poles in the USSR dropped by 165,000 in that period as the Soviet statistics indicate. Depending on size of their families, the fate of around 200,000–250,000 Poles was sealed after they have been purposely left with nothing to live on.