1890 Treaty of London defining Portuguese colonial borders

Background. The treaty emerged from an Anglo-Portuguese crisis following the 1890 British Ultimatum. Lord Salisbury demanded Portuguese troop withdrawal from Mashonaland, Matabeleland, and the Shire-Nyasa region. This followed a British refusal of arbitration and pressure from Cecil Rhodes' British South Africa Company. The 1890 treaty attempted to fix boundaries, but its failure to be ratified led to continued conflict and a new agreement in 1891.

Terms and Ratification. Signed on 20 August 1890, the treaty defined territorial limits for Angola and Mozambique. However, it was never ratified by the Portuguese Parliament. The unratified status meant that areas allocated to Portugal were later reassigned to the British South Africa Company in the 1891 treaty. Portugal received more land in the Zambezi valley as compensation for these losses.

Aftermath. The 1890 ultimatum soured Anglo-Portuguese relations. Armed clashes in Manicaland ceased only after the 1891 treaty reassigned territories. The 1891 treaty, signed in Lisbon, fixed borders, allowed navigation on the Zambezi and Shire rivers, and permitted a British port at Chinde. The 1890 ultimatum was later said to be one of the main causes of the failed republican revolt of 31 January 1891.