劉永福
French explorers followed the course of the Red River through northern Vietnam to its source in Yunnan, arousing hopes for a profitable trade route with China that could bypass the treaty ports of the Chinese coastal provinces. The main obstacle to this idea, the Black Flag Army – a well-organized bandit force led by the formidable Liu Yongfu – was levying exorbitant "taxes" on Red River trade between Sơn Tây and Lào Cai on the Yunnan border.