Weird how the internet can tell me 1.6 million people died in gulags but there is no hazy estimate of how many folks have died in US prisons other than a report for 2001-2014 which hilariously misorders cause of death to downplay homicide and 'missing'.
I also want to point out that restricting this to "20th century" vastly favors the USA due to its most brutal period of industrialization and slavery being outside the window