5·1 year ago- Mark Tauger documents it https://newcoldwar.org/archive-of-writings-of-professor-mark-tauger-on-the-famine-scourges-of-the-early-years-of-the-soviet-union/
- This is the Polish invasion of the USSR in the early 1920s. Look at the parts of Ukraine and Belorussia they took, linguistic maps of that area, and compare to the regions taken back by the USSR under the MR pact. As for the brutality of the regime it’s not well covered in English language history, mostly it’s covered in polish, Ukrainian, and Russian language sources. I know Timothy Snyder covers it in bloodlands but he’s so closely aligned with the modern Ukrainian nationalist movement that I don’t like to recommend him. It should be easy enough to find some English language history of the militaristic polish regime of the 1930s.