So to understand Apartheid you need understand some developments in South Africa History of course.

The first is the Anglicization of South Africa. After the British, they began to marginilize the Afrikaner/Boer population. This lead to the spread of Afrikaner from the Cape to first Natal and then the interior establishing both the OSF and the ZAR. This was done first and foremost to escape the British threat.(Hermann Giliomee The Afrikaners:Biography of a People)

The Next is the Boer Wars, especially the 2nd, which lead to a Boer defeat, and a greater impetus for the preservation of Boer culture. This is where Apartheid is truly born.

Even Afrikaner "moderates" like Jan Smuts lament that "There are years of great danger ahead before us, partly because people have fallen so deep, so fathomlessly deep, into poverty and misery, partly because everything will be done by the other side, through their education system, and otherwise, to anglicise the generation now growing up"

Now Smuts becomes a supporter of Anglo-capitalism in South Africa later, but he echoes the sentiment that many feel. That the Brits and the economic system that they imported were a threat to the Afrikaner identity.

Geoffrey Cronje, who was one of the main architechts of Apartheid as an ideology argued that in any scenario where the Afrikaners were a minority, that they would be swamped and cease to exist due to the sheer numbers of Brits and Africans. He advocated for total partition, that is that a seperate black polity would be created alongside an Afrikaner polity, and therefore the Afrikaner race would be preserved. Cronje is probably the most explicit to this as the goal, but it is very true that this was what Apartheid's supporters wanted, and the preservation of the Afrikaner identity was paramount. (Erich Louw The Rise, Fall, and Legacy of Apartheid)

This was to be contrasted with the Blaaskaap(white supremacy) of Anglo-capitalism and Smuts that places all Whites above blacks economically. Rather Apartheid was to create parallell and seperate societies.

So prior to the mid-1950s, Apartheid was centred around preservation of Afrikaner identity and the elimination of Anglo-imperialism in South Africa.

By the 1950s and certainly by the 1960s and the reign of Hendrik Voerwoerd things changes.

Hendrik Voerwoerd expresses Apartheid as "good neighborliness" in a speech, and what he means is that South Africa helps its black neighbors develop so that they ccan be self reliant apart from the rest of South Africa, ignoring the fact that even under the Bantustan plan, which meant to resettle black South Africans on reserves away from white cities with the goal of eventual independence, South Africa would still be dependent on labour.

It is now a good time to mention that even to today, historians of Apartheid like myself spend a ton of time arguing on wether or not Apartheid was really about labour, in so far as keeping a source of cheap labour to underpin white society, or if it was truly about race. Certainly there are good arguments both ways, especially if you consider that British abolition legislation and Black enfranchisement was perhaps the biggest contention between Afrikaners and Anglos in the Cape.

Now that being said the idea of Apartheid as Neighborliness is what was perpetuated at least until Sharpeville.

After Sharpeville and the beggining of an armed and "communist" resistance against the state it empowered South Africa to become more draconian and degrade into a police state, and use the specter of communism to justify its actions.

Additional sources

Brian Lapping Apartheid: A History

Joe Slovo Joe Slovo the unfinished Autobiography

Dennis Goldberg A Life for Freedom

Stephen Clingman Bran Fischer: Afrikaner Revolutionary

The Freedom Charter by the ANC