The ZAR recognised this proclamation as an act of aggression, and resisted. Instead of declaring war, the country decided to send a delegation to the United Kingdom and the United States, to protest. This did not have any effect, and the First Boer War formally broke out on 20 December 1880. The First Boer War was the first conflict since the American Revolution in which the British had been decisively defeated and forced to sign a peace treaty under unfavourable terms.