Soviet population group to be sentenced in this manner. After the approval of the entire "album", the executions were carried out immediately. This procedure was also used later on in other mass operations of the NKVD. The "Polish Operation" was a second in a series of national operations of the NKVD, carried out by the Soviet Union against ethnic groups including Latvian, Finnish, German, and Romanian, based on a theory about an internal enemy (i.e., the fifth column), labelled as the "hostile capitalist surrounding" residing along its western borders. In the opinion of historian Timothy Snyder, this fabricated justification was intended only to cover-up the state-sanctioned campaign of mass-murder aiming to eradicate Poles as a national (and linguistic) minority group. Another possible cause, according to Snyder, might have sprung from the necessity to explain the Holodomor, the Soviet-made famine in Ukraine, which required a political scapegoat. A top Soviet official, Vsevolod Balitsky, chose the Polish Military Organization which was disbanded in 1921. The NKVD declared that it continued to exist. Some Soviet Poles were tortured in order to confess to its existence, and denounce other individuals as spies. Meanwhile, the Communist International helped by revisiting its files in search of Polish members, producing another bountiful source of made-up evidence. Targets of the operation The operation took place approximately from August 25, 1937 to November 15, 1938. The largest group of people with a Polish background, around 40 percent of all victims, came from Soviet Ukraine, especially from the districts near the border with Poland. Among them were tens of thousands of peasants, railway workers, industrial labourers, engineers and others. An additional 17 percent of victims came from Soviet Byelorussia. The rest came from around Western Siberia and Kazakhstan, where exiled Poles had lived since the Partitions of Poland, as well as from the southern Urals, northern Caucasus and the rest of Siberia, including the Far East. The following categories of people were arrested by the NKVD during its Polish Operation, as described in Soviet documents: All "antisoviet and nationalistic elements" from districts and region in the USSR where there existed a Polish community. All immigrants from the Second Polish Republic. Political exiles from Poland. Former and present members of the Polish Socialist Party and other non-communist Polish political parties. All prisoners of war from the Polish-Soviet war remaining in the Soviet Union. Members of the Polish Military Organisation listed in