Overview
Three centuries of division did more for Chinese dress than most unified dynasties. With non-Han rulers in the north and refugee Han courts in the south, two clothing traditions ran in parallel and steadily borrowed from each other — and the practical northern outfit ended up in the mainstream, which is where the Tang round-collar robe comes from.
Key garments and style
The northern garment is the kuzhe: a narrow-sleeved jacket worn with trousers, sometimes bound below the knee, cut for riding. It spread well beyond the steppe elite and was worn by Han people across the north.
The southern courts went the other way, into loose robes with very wide sleeves worn open and loosely belted — the Wei-Jin manner, associated with scholars who made unconstraint a philosophical position as much as a style.
The most explicit act of the period runs against the drift. In the 490s Emperor Xiaowen of the Northern Wei ordered his court to adopt Han dress, language and surnames, banning the Xianbei clothing his own dynasty had come in wearing — sinicisation imposed by an emperor on his own people.
Buddhism arrived along the same routes, bringing monastic robes and a new repertoire of motifs into Chinese textiles.
Transition
The Sui reunified north and south and built one court standard from both, keeping the northern round-collar robe as official dress.