The Black Flag Army (; ) was a splinter remnant of a bandit group recruited largely from soldiers of ethnic Zhuang background, who crossed the border in 1865 from Guangxi, China into Upper Tonkin, then part of the Empire of Annam (Vietnam). Although brigands, they were known mainly for their fights against the invading French forces, who were then moving into Tonkin. With the sanction of both Vietnamese and Chinese authorities, the Black Flags joined the Vietnamese regular forces, stemming French encroachment beyond the Red River Delta. The Black Flag Army is so named because of the preference of its commander, Liu Yongfu, for using black command flags.