Colonial Nigeria refers to the area of West Africa, which became the modern day Nigeria, during the time British rule in the 19th and 20th centuries. British influence began with prohibition of slave trade to British subjects in 1807. The resulting collapse of African slave trade led to the decline and eventual collapse of the Edo Empire. Britain annexed Lagos in 1861 and established the Oil River Protectorate in 1884. British influence in the Niger area increased gradually over the 19th century, but Britain did not effectively occupy the area until 1885. Other European powers acknowledged Britain's power over the area in the 1885 Berlin Conference.