Following a industrial boom after the second world war, South African began to have the potential to emerge as a geopolitical (and economic, secondarily) to the traditional imperial powers,
The apartheid regime acted as a causus belli for them (the traditional imperial powers) to impose sanctions.
A comrade from SA summarized it to me as follows: There is a partial transition from settler-colonialism to neo-colonialism, wherein segments of the old apartheid upper class along with the emerging black bourgeoisie and petty bourgeoisie are integrating into a semi- comprador structure.
Some evidence of this is all that weapons grade uranium that was produced that was not put into a nuclear weapons program. In fact, even civilian nuclear power production in SA has remain stagnant.
The same can be said for the structure of the economy: It remains highly dependent on mining and does not even significantly mass produce mining equipment.