Simple. The radicals started taking over academia in several waves, starting at least as early as the ‘30s. The most recent visible radical disruption was in the ‘60s. They created studies and majors that attracted like-minded socialists, and eventually radicalized and took over other departments. A tipping point was reached.
As usual, conservatives playing by the rules didn’t know what hit them. Too late!
All part of the plan, clearly announced by the likes of Ayers and Dohrn 40 years ago.
I think you are right but I think it goes back way before the 30’s. I have always suspected the French Revolution was an early leftist plot.
I also suspect that the radical republicans of the US in the middle 19th century were very close to Communists. I have read more than once that Karl Marx sent an observer of the War Between the States. He reportedly was very fond of Lincoln.