It got me thinking,I think that the latest is the North South Dynasty period.From my readings,it seems that aristocratic clans were the main supporters of regionalism.Until the reign of Wu Zetian,they dominated government posts and sponsored coups and rebellions in different government regimes.They despised government interference in local affairs and unlike the gentry of later periods actually had large political influence,money and soldiers to attempt rebellions or coups when the different aristocratic clans banded together.They also seem to despise clans from different areas.For example,they aristocrats from Guanzhong seems to be one block,those in the North China Plain seems to be another while those from the south of the Yangtze formed a third bloc.