The Nazi police state was built quickly. Dachau opened on 22 March 1933, and 'protective custody' without trial became routine; the Gestapo and the SS Security Service were fused under Himmler, and the People's Court, established in 1934, replaced ordinary due process with political justice (Evans 2003; Shirer 1960). After 1941 the apparatus of camps and mobile killing units extended into occupied Europe, where the extermination camps — Chełmno, Bełżec, Sobibór, Treblinka, Auschwitz-Birkenau and Majdanek — carried out the genocide (USHMM). Auschwitz-Birkenau alone killed about 1.1 million people, of whom about one million were Jews (USHMM).
The Soviet police state had a longer pedigree. The Cheka became the NKVD, and Article 58 of the criminal code turned political dissent into a criminal category; show trials and the mass operations of 1937–38 produced about 1.5 million arrests and some 680,000 executions in NKVD records (Getty, Rittersporn & Zemskov 1993; Conquest 1990). The Gulag became a permanent institution: up to about 2.5 million people were held in the camps in the early 1950s, and some 18 million passed through the system between 1929 and 1953 (Applebaum 2003). Its scale was first forced into public view by survivors' testimony (Solzhenitsyn 1973–76). Katyn, in April–May 1940, added about 22,000 murdered Polish officers to the record (Snyder 2010).
The shared element is not the identity of the victims but the position of violence in government. In both states the police answered to the party rather than to law, confession was obtained by torture, the camps were permanent rather than exceptional, and the category of 'enemy' could be widened by decree. The Soviet regime also deported whole nations: the Crimean Tatars (about 191,000 in 1944), the Chechens and Ingush (about 400,000–500,000 in 1944) and the Volga Germans (about 400,000 in 1941) were moved by force under Stalin (Naimark 2010). What differs is the selection principle — race in one case, class and political loyalty in the other — and that difference is the subject of the next section.