The Gulag (/ˈɡuːlɑːɡ/, UK also /-læɡ/; Russian: ГУЛаг, romanized: GULag, [ɡʊˈlak] (About this soundlisten), acronym of Main Administration of Camps, Russian: Главное управление лагерей)[a] was the government agency in charge of the Soviet forced-labour camp set up under Vladimir Lenin[11] and reached its peak during Joseph Stalin's rule from the 1930s to the early 1950s. English-language speakers also use the word gulag to refer to any forced-labour camp in the Soviet Union, including camps which existed in post-Stalin times. The camps housed a wide range of convicts, from petty criminals to political prisoners. Large numbers were convicted by simplified procedures, such as by NKVD troikas or by other instruments of extrajudicial punishment. The Gulag is recognised as a major instrument of political repression in the Soviet Union. The agency was first administered by the GPU, later by the NKVD and in the final years by the Ministry of Internal Affairs (MVD). The Solovki prison camp, the first corrective labor camp constructed after the revolution, was established in 1918 and legalised by a decree "On the creation of the forced-labour camps" on April 15, 1919. The internment system grew rapidly, reaching a population of 100,000 in the 1920s. According to Nicolas Werth, author of The Black Book of Communism, the yearly mortality rate in the Soviet concentration camps strongly varied, reaching 5% (1933) and 20% (1942–1943) while dropping considerably in the post-war years (about 1 to 3% per year at the beginning of the 1950s). The emergent consensus among scholars who utilize official archival data is that of the 18 million who were sent to the Gulag from 1930 to 1953, roughly 1.5 to 1.7 million perished there or as a result of their detention. However, some historians question the reliability of such data and instead rely heavily on literary sources that come to higher estimations. Archival researchers have found "no plan of destruction" of the gulag population and no statement of official intent to kill them, and prisoner releases vastly exceeded the number of deaths in the Gulag.