In 1881, China declared sovereignty over Annam or Vietnam, sending troops down the Red River to occupy its northern region, Tonkin. France, angered by continuing Vietnamese persecution of Christian missionaries, renewed its colonial expansionism in Indochina (Vietnam, Laos, and Cambodia), which China opposed. French captain Henri Laurent Riviere (1827-83) was sent with a small force to Tonkin's administrative center, Hanoi, to evict the Chinese and to subdue the rebel "Black Flag Prirates." He captured the Hanoi fortress, Nam Dinh's coast, and the Hon Gay coal mine. During a Vietnamese counterattack, Riviere was killed. French reinforcements were sent to the area, and France obtained a Vietnamese agreement on a treaty ceding Tonkin (1882). When China renounced the agreement, the French seized Haiphong and Hanoi and bombarded the Vietnamese capital of Hue (1883). During the fighting, both sides negotiated and finally signed a treaty (August 25, 1883) that recognized French protectorates over northern Vietnam (Tonkin) and central Vietnam (Annam); southern Vietnam (Cochin China) was already under French control. Ten years later Siam relinquished to the French its claims to Laos, which was incorporated into a federation known as French Indochina.