A vast system of prisons, camps, and exile settlements, the Gulag was one of the defining attributes of the Stalinist Soviet Union and one of the most heinous examples of mass incarceration in the twentieth century, combining the functions of a standard prison system with the goal of isolating and punishing alleged enemies of the Soviet regime. it stretched throughout the Soviet Union, from central Moscow to the farthest reaches of Siberia. From its creation in 1930 to its partial dismantling in the mid-1950s, approximately 25 million people passed through the Gulag. Prisoners and exiles were...