The foreign relations of the Dominions were initially conducted through the Foreign Office of the United Kingdom: Canada created a Department of External Affairs in 1909, but relations with other governments cotinued to be conducted through British diplomatic missions, although a Canadian War Mission in Washington, D.C. dealt with supply matters in 1918-21. Britain's declaration of war against Germany in August 1914 was deemed to apply to all territories of the Empire, provoking a brief anti-British insurrection in South Africa later that year.
Although the Dominions had had no formal voice in declating war, each was included among the signatories of the June 1919 peace Treaty of Versailles, which had been negotiated by a British-led united Empire delegation. Diplomatic autonomy soon followed, with the US-Canadian Halibut Fisheries Agreement (March 1923) marking the first international treaty negotiated and concluded entirely independently by a former colony. The principle of independence in foreign relations was formally ratified at the Imperial Conference of October 1926 and enshrined in the Statute of Westminster, adopted by the British Parliament in December 1931.
The term "Dominion" fell out of use after India's adoption of a republican Constitution in November 1949, though all members of what was subsequently styled the Commonwealth agreed to accept the British monarch as head of the organisation. Ireland had formally ceased to be a member seven months earlier upon becoming the Republic of Ireland.