A secret Anglo-Portuguese declaration that secured British support for Portuguese colonies while binding Portugal to aid Britain in the Second Boer War.
Key Facts
- Signed
- 14 October 1899
- British signatory
- Lord Salisbury, Prime Minister
- Portuguese signatory
- Marquis of Soveral, Ambassador
- Named after
- Treaty of Windsor (1386)
- Earlier treaties reaffirmed
- Treaties of 1642 and 1661
- Context
- Preceded Second Boer War (1899–1902)
By the Numbers
Location
Cause → Event → Consequence
Anglo-Portuguese relations in Africa had been strained by the 1890 British Ultimatum, which blocked Portugal from linking Angola and Mozambique, leading to the Anglo-Portuguese Treaty of 1891. Further tension arose from an 1898 Anglo-German agreement that contemplated dividing Portuguese African colonies between Britain and Germany, threatening Portugal's colonial holdings.
On 14 October 1899, British Prime Minister Lord Salisbury and the Portuguese Ambassador Marquis of Soveral secretly signed the declaration in London, reaffirming prior treaties from 1642 and 1661. Britain pledged to defend Portuguese colonies against present and future enemies, while Portugal agreed not to declare neutrality in the Second Boer War and to block Boer arms and troop movements through Lourenço Marques and Mozambique.
The agreement secured Portuguese colonial integrity under British protection and denied the Boers a logistical corridor through Portuguese Mozambique. By preventing arms and troop transit via Lourenço Marques to the Transvaal, the treaty gave Britain a strategic advantage in the Second Boer War and reinforced the long-standing Anglo-Portuguese alliance.
Political Outcome
Britain guaranteed defence of Portuguese colonies; Portugal agreed to withhold neutrality and block Boer military access through Mozambique during the Second Boer War.
Anglo-Portuguese relations strained by 1890 ultimatum and 1898 Anglo-German colonial partition understanding
Alliance reaffirmed; Portugal's colonies secured under British protection in exchange for Boer War cooperation