million. Population transfers Population transfer in the Soviet Union may be divided into the following broad categories: deportations of "anti-Soviet" categories within the population, who were often classified as "enemies of the workers"; deportations of nationalities; labor force transfer; and organised migrations in opposite directions in order to fill the ethnically cleansed territories. In most cases their destinations were underpopulated and remote areas (see Involuntary settlements in the Soviet Union). Entire nations and ethnic groups were collectively punished by the Soviet Government for their alleged collaboration with the enemy during World War II. At least nine distinct ethnic-linguistic groups, including ethnic Germans, ethnic Greeks, ethnic Poles, Crimean Tatars, Balkars, Chechens, and Kalmyks, were deported to remote and unpopulated areas of Siberia (see sybirak) and Kazakhstan. Koreans and Romanians were also deported. Mass operations of the NKVD were needed to deport hundreds of thousands of people. Gulag The Gulag "was the branch of the State Security that operated the penal system of forced labour camps and associated detention and transit camps and prisons. While these camps housed criminals of all types, the Gulag system has become primarily known as a place for political prisoners and as a mechanism for repressing political opposition to the Soviet state." Repressions in annexed territories During the early years of World War II, the Soviet Union annexed several territories in Eastern Europe as a consequence of the German–Soviet Pact and its Secret Additional Protocol. Baltic States In the Baltic countries of Estonia, Latvia and Lithuania, repressions and mass deportations were carried out by the Soviets. The Serov Instructions, "On the Procedure for carrying out the Deportation of Anti-Soviet Elements from Lithuania, Latvia, and Estonia", contained detailed procedures and protocols to observe in the deportation of Baltic nationals. Public tribunals were also set up to punish "traitors to the people": those who had fallen short of the "political duty" of voting their countries into the USSR. In the first year of Soviet occupation, from June 1940 to June 1941, the number confirmed executed, conscripted, or deported is estimated at a minimum of 124,467: 59,732 in Estonia, 34,250 in Latvia, and 30,485 in Lithuania. This included 8 former heads of state and 38 ministers from Estonia, 3 former heads of state and 15 ministers from Latvia, and the then president, 5 prime ministers and 24 other ministers from Lithuania. Poland Romania Post-Stalin era (1953–1991) After Stalin's death, the