This is a little confusing, because the flag on the left is the flag of the Soviet Union. But the Soviet Union was (a) a confederation of countries and (b) not fully incorporated until 1955 under the Warsaw Pact. It's a bit weird to count "prisoners under the USSR" as a political block, but only count "prisoners under the United States" as a single country. Would make more sense to count all the prisoners in all the NATO countries against their populations, as point of comparison.

Also, inevitably has to be asked, because "Black Book" assholes love doing this, but... 1950 was very close to the end of WW2. So, how many of these 2.5M prisoners were wearing little swastika armbands five years earlier?