The British Conquest of Benin

In 1897 a British force took Benin City and brought the kingdom of Benin under British rule. According to the Library of Congress country study, the expedition followed the killing of a British consul and his party who were travelling to the city. Wikipedia's article on Oba Ovonramwen gives more detail: relations had worsened after a treaty of 1892 that the British read as limiting Benin's independence, and in January 1897 the acting consul-general, James Phillips, set out for Benin although the oba had asked him to postpone the visit; a group of Benin chiefs, despite objections attributed to the oba, attacked the party near Ugbine and killed Phillips and most of its European members. (Wikipedia's general history of Nigeria dates Phillips's journey to 1896 and calls him vice-consul.) A punitive expedition under Admiral Rawson followed in February 1897.

The background was a struggle over trade and authority. According to Wikipedia's article on Oba Ovonramwen, a treaty of 1892, negotiated by the vice-consul Henry Gallwey, was read by the British as limiting Benin's independence, while Ovonramwen continued to enforce Benin's trade restrictions and royal monopolies. As British officials and European merchants pressed for access to Benin's markets, senior protectorate officers were by 1896 openly considering removing him, and in November 1896 James Phillips sought approval to depose him. Benin, about 150 kilometres east of Lagos, was one of the largest kingdoms in what is now Nigeria (Wikipedia's history of Nigeria), and the Library of Congress country study notes that the consul's party was on its way to investigate reports of ritual human sacrifice in the city.

The British destroyed the oba's palace, and the oba was sent into exile; Benin was then governed indirectly through a council of chiefs (country study). Wikipedia records that the palace was burnt and its bronze sculptures were taken and later auctioned in Europe to pay for the expedition. The country study notes that the conquest completed the British occupation of south-western Nigeria.