Don't forget the Great Leap Forward.
It is also an important event.
The Southern and Northern Dynasties showed such a high level of polarization between North and South that northerners and southerners referred to each other as barbarians; the Mongol Yuan Dynasty also made use of the concept: Yuan subjects were divided into four castes, with northern Han Chinese occupying the second-lowest caste and southern Han Chinese occupying the lowest one.
Traditional Yi society in Yunnan was caste based. People were split into the Black Yi (nobles, 5% of the population), White Yi (commoners), Ajia (33% of the Yi population) and the Xiaxi (10%). Ajia and Xiaxi were slave castes. The White Yi were not slaves but had no freedom of movement. The Black Yi were famous for their slave-raids on Han Chinese communities. After the 1959 some 700,000 slaves were freed.
But of course, all this is not taught in the Glorious Era of Peasants and Workers since it would be an embarrassment.