The growth of the British Empire in the 19th century, to its territorial peak in the 1920s, saw Britain acquire nearly one quarter of the world's land mass, including territories with large indigenous populations in Asia and Africa. From the mid-nineteenth century to the early twentieth century, the larger settler colonies – in Canada, Australia, New Zealand and South Africa – first became self-governing colonies and then achieved independence in all matters except foreign policy, defence and trade. Separate self-governing colonies federated to become Canada (in 1867), Australia (in 1901), South Africa (in 1910), and Rhodesia (in 1965). These and other large self-governing colonies had become known as Dominions by the 1920s. The Dominions achieved almost full independence with the Statute of Westminster (1931). a process of decolonisation following the Second World War, most of the British colonies in Africa, Asia and the Caribbean gained independence. Some colonies became Commonwealth realms, retaining the British monarch as their own head of state. Most former colonies and protectorates became member states of the Commonwealth of Nations, a non-political, voluntary association of equal members, comprising a population of around 2.2 billion people.