At the behest of General MacArthur, Japan carried out a "Red Purge" in which communists in the education system were kicked out of their positions. This included universities.
No wonder Japan has much less problems with commie extremists than the rest of the industrialized road.
Too bad the commie purge didn’t work in the US. McCarthy and others tried. Commies were too embedded in the US. Very embedded. So now the purge is going to be wild.