The concept for this AU is that in 1922 Southern Rhodesia votes yes in a plebiscite to join the Union of South Africa. This leads to changes in events that sees a new federal Union constitution that accommodates the then declining population of Africans in tribal nations alongside the white and coloured provinces. These changes see the UK transfer to the union several protectorates and the League of Nations replace the South African mandate over South West Africa to full sovereignty. These things were all considered in the real world in the 1900s to 1930s.
The result is a Union of South Africa by 1948 that includes the six advanced provinces (Cape of Good Hope, Natal, Orange Free State, Transvaal, Rhodesia, South West Africa) and around 30 African tribal nations. Which includes Bechuanaland, Lesotho, Swaziland and Northern Rhodesia. Each subject of the union is a citizen of a particular province or tribal nation and seats in the Union Parliament are decided upon based on each province or tribal nations financial contribution to the central union. Because of the very low tax base raised from the tribal nations (typically just a hut tax of £1 per family per annum) before the 1960s this means they generally only have the minimum representation.
Union of South Africa (WIP) 1960
Light green areas are the advanced provinces and dark green-grey areas the African tribal nations. The medium green-grey areas are federal land (parks and reserves).
Because of the incorporation of Rhodesia and the maintenance of the Cape Coloured as citizens of the Cape of Good Hope and the token representation of the tribal nations the Afrikaner Nationalist movement is never able to gain control over the South African government. Apartheid is never introduced and some of the more extreme elements of segregation law are repealed in the 1960s and 70s. The United Party remains the dominant force in South African politics well into the 1990s with the reintegration of the Afrikaner Nationalists in the 1970s.
Without the Nationalist government South Africa remains focused on wider Western defence needs in the 1950s and therefore invests heavily in building up the Navy after the Korean War. Like Australia and Canada the newly named Royal South African Navy acquires a carrier force in the late 1950s. Things go sour in the 1960s and 70s as the previously declining Black African population booms and newly development African nationalist political movements demand majority rule and the destruction of the settler society. While the African nationalists are able to garner huge political support in the Soviet bloc and developing world against South Africa the representative political nature of the Union makes it difficult to develop that opposition in western states. Especially as reform allows the tax revenue of tribal nation citizens living in the provinces to be used in their home land’s political representation calculation. While this still keep the black vote very much a minority until the 1990s the lack of overt racist legislation in the Union does not see the development of worldwide anti Apartheid movement. Many liberal governments in the west join in condemnation of South Africa from time to time, especially as military action against the African nationalists heats up in the 1970s and 80s but there is no UN arms embargo and significant ostracizing of South Africa.