<Tr> <Td> South Africa </Td> <Td> </Td> </Tr> <Tr> <Td_colspan="2"> Today part of </Td> <Td> Namibia South Africa </Td> </Tr> <P> The Union of South Africa (Dutch: Unie van Zuid - Afrika, Afrikaans: Unie van Suid - Afrika) is the historic predecessor to the present - day republic of South Africa . It came into being on 31 May 1910 with the unification of four previously separate British colonies: the Cape, Natal, Transvaal and Orange River colonies . It included the territories formerly part of the Boer republics annexed in 1902, the South African Republic and the Orange Free State . </P> <P> Following the First World War, the Union of South Africa was granted the administration of South West Africa (formerly a German colony and today the sovereign state of Namibia) as a League of Nations mandate, which became treated in most respects as if it were another province of the Union, but never was formally annexed . </P>

When was the union of south africa formed