That's one possible view, of course. The wrinkle is that the establishment of the Trekker republics (there were at least five, excluding the Hollandse Kaap) can be seen as a species of local imperialism, or at least conquest. The interior was not entirely a terra nullius. The story still needs to be told of how the Trekkers earnestly tried to negotiate with the indigenes for land. However, within a few decades they were all overwhelmed by a global imperial power.
A change of heart in the global imperial power resulted in greater local government for the local European descendants, with eventual unfettered hegemony in the erstwhile imperial lands. Interestingly, a number of ethnically-based Black states were established (Basotholand, Swaziland, Bechuanaland) which eventually also obtained their full independence.