British Ultimatum

The 1890 British Ultimatum was an ultimatum by the British government delivered on 11 January 1890 to Portugal. The ultimatum forced the retreat of Portuguese military forces from areas which had been claimed by Portugal on the basis of historical discovery and recent exploration, but which the United Kingdom claimed on the basis of effective occupation. Portugal had attempted to claim a large area of land between its colonies of Mozambique and Angola including most of present-day Zimbabwe and Zambia and a large part of Malawi, which had been and included in Portugal's "Rose-coloured Map".

It has sometimes been claimed that the British government's objections arose because the Portuguese claims clashed with its aspirations to create a Cape to Cairo Railway, linking its colonies from the south of Africa to those in the north. It seems unlikely, as in 1890 Germany already controlled German East Africa, now Tanzania, and Sudan was independent under Muhammad Ahmad. Also, the British government was pressed into taking action by Cecil Rhodes, whose British South Africa Company was founded in 1888 south of the Zambezi and the African Lakes Company and British missionaries to the north.

At the start of the 19th century, the Portuguese presence in Africa south of the equator was limited in Angola to Luanda and Benguela and a few outposts, the most northerly of which was Ambriz and in Mozambique to the Island of Mozambique, several other coastal trading posts as far south as Delagoa Bay and the virtually independent Prazo estates in the Zambezi valley The first challenge to Portugal's wider claims came from the Transvaal Republic, which in 1868 claimed an outlet to the Indian Ocean at Delagoa Bay. Although in 1869, Portugal and the Transvaal reached agreement on a border under which all of Delagoa Bay was Portuguese, the UK then lodged an objection, claiming the southern part of that bay. The claim was rejected after arbitration by President MacMahon of France. His award made in 1875 upheld the border agreed in 1869. A second challenge came from the foundation of a German colony at Angra Pequena, now known as Lüderitz in Namibia in 1883. Although there was no Portuguese presence there, Portugal had claimed it on the basis of discovery.

...
Wikipedia