According to a scholarly article cited here,
there were between 2 million and 2.5 million people in Soviet prisons
and camps every year between 1938 and 1953. The current population
in US jails plus prisons also exceeds 2 million (Bureau
of Justice Statistics). This comparison has not escaped people’s
notice, as a Google search of "Gulag" and "prison population"
Of course, there are differences between prisons in the US and in
Stalin’s Soviet Union. First, the vast majority of incarcerated people
in America have committed crimes, and they have received due process,
albeit flawed in some cases. Second, conditions in US prisons are
better than conditions in Siberian work camps. Third, our incarceration
rate is lower as a percentage of our population, although it may be
higher in some inner-city neighborhoods today than it was in the USSR
circa 1950. Fourth, the modern rationale for mass incarceration (reducing
crime) is better than Stalin’s reason (terrorizing people into submission
to him personally). Above all, the Soviet terror involved mass killing
as well as imprisonment.
Nevertheless, at the very least, the incarceration of 2 million Americans—with
collateral damage to their victims, and to their families and communities—represents
a social failure that’s unique in today’s world and comparable to
the disasters under Stalin.