I'm sure you can put any date in here and come up with interesting stuff, but for September 12 here are some things that popped out at me -
490 BC Traditional date of the Battle of Marathon, where a small Athenian force defeats the Persian Empire
1950 Belgian government dismisses all communist civil servants
1958 US Supreme Court orders the all-white Central High School in Little Rock, Arkansas to integrate
1958 US performs nuclear test at Nevada Test Site
1974 Coup overthrows Ethiopian Emperor Haile Selassie on Ethiopia's national day
https://www.onthisday.com/events/september/12