When did the campaign of political  repression that Mikhail Demichev was arrested during occur?
Great Purge The Great Purge or the Great Terror (Russian: Большо́й терро́р ) was a campaign of political repression in the Soviet Union which occurred from 1936 to 1938. It involved a large-scale purge of the Communist Party and government officials, repression of peasants and the Red Army leadership, widespread police surveillance, suspicion of "saboteurs", "counter-revolutionaries", imprisonment, and arbitrary executions. Mobile gas vans were invented to execute people without trial. In Russian historiography, the period of the most intense purge, 1937–1938, is called Yezhovshchina (Russian: Ежовщина ; literally, "Yezhov phenomenon", commonly translated as "times of Yezhov" or "doings of Yezhov"), after Nikolai Yezhov, the head of the Soviet secret police, the NKVD, who was later killed in the purge. It has been estimated that 600,000 people died at the hands of the Soviet government during the Purge.
1980 Turkish coup d'état The 12 September 1980 Turkish coup d'état (Turkish: "12 Eylül Darbesi" ), headed by Chief of the General Staff General Kenan Evren, was the third coup d'état in the history of the Republic, the previous having been the 1960 coup and the 1971 "Coup by Memorandum". The 1970s in Turkey were marked by right-wing/left-wing armed conflicts, in the context of the Cold War. To create a pretext for a decisive intervention, the Turkish military allowed these conflicts to escalate; some say they actively adopted a strategy of tension. The violence abruptly stopped afterwards, and the coup was welcomed by some for restoring order. In total, 50 people were executed, 500,000 were arrested and hundreds died in prison.