The ability of the Dominions to set their own foreign policy, independent of Britain, was recognised at the 1923 Imperial Conference. Britain's request for military assistance from the Dominions at the outbreak of the Chanak Crisis the previous year had been turned down by Canada and South Africa, and Canada had refused to be bound by the 1923 Treaty of Lausanne. After pressure from Ireland and South Africa, the 1926 Imperial Conference issued the Balfour Declaration, declaring the Dominions to be "autonomous Communities within the British Empire, equal in status, in no way subordinate one to another" within a "British Commonwealth of Nations". This declaration was given legal substance under the 1931 Statute of Westminster. The parliaments of Canada, Australia, New Zealand, the Union of South Africa, the Irish Free State and Newfoundland were now independent of British legislative control, they could nullify British laws and Britain could no longer pass laws for them without their consent. Newfoundland reverted to colonial status in 1933, suffering from financial difficulties during the Great Depression. Ireland distanced itself further from Britain with the introduction of a new constitution in 1937, making it a republic in all but name.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When was the right of Dominions to determine their own foreign policy recognized?
1923