Though the modern Commonwealth is just 60 years old, the idea took root in the 19th century.
In 1867, Canada became the first colony to be transformed into a self-governing 'Dominion', a newly constituted status that implied equality with Britain. The empire was gradually changing and Lord Rosebury, a British politician, described it in Australia in 1884 as a "Commonwealth of Nations".
Other parts of the empire became Dominions too: Australia (1901), New Zealand (1907), South Africa (1910) and the Irish Free State (1922). All except the Irish Free State (that did not exist at the time) participated as separate entities in the First World War and were separate signatories to the Treaty of Versailles in 1919. Subsequently, they became members of the League of Nations.
After the end of the First World War, the Dominions began seeking a new constitutional definition and reshaping their relationship with Britain. At the Imperial Conference in 1926, the prime ministers of the participating countries adopted the Balfour Report which defined the Dominions as autonomous communities within the British Empire, equal in status, in no way subordinate to one another in any aspect of their domestic or external affairs, though united by common allegiance to the Crown, and freely associated as members of the British Commonwealth of Nations.
This definition was incorporated into British law in 1931 as the Statute of Westminster. It was adopted immediately in Canada, the Irish Free State, Newfoundland (which joined Canada in 1949) and South Africa. Australia and New Zealand followed. India, Britain's largest colony at the time, became a Dominion at independence in 1947 and remained so until January 1950, when the Indian Republic was born.
Commonwealth at 60