Union of South Africa

The Union of South Africa (Dutch: Unie van Zuid-Afrika; Afrikaans: Unie van Suid-Afrika, ) was a British Dominion and, later, a Commonwealth realm in southern Africa from 1910 to 1961. It was the historical predecessor to the present-day Republic of South Africa. It came into existence on 31 May 1910 with the unification of the Cape, Natal, Transvaal, and Orange River colonies. It included the territories that were formerly part of the South African Republic and the Orange Free State.

Following World War I, the Union of South Africa was a signatory of the Treaty of Versailles and became one of the founding members of the League of Nations. It was mandated by the League with the administration of South West Africa (now known as Namibia). South West Africa became treated in most respects as another province of the Union, but it never was formally annexed.