There were a fuck ton of supremacists on the face of the planet during the 50s, and believe it or not, just because you're "white" doesn't mean you're of the same race, boers and brits have different attitudes and tendencies, so that caused some conflict. Another thing to consider, the temptation to judge somebody based on their nationality or group affiliation becomes 600% more tempting the moment members of that group tend to do that towards *your* group, and both Boers AND the British who made up like 99% of the white population had very strong nationalistic tendencies; The brits cus they had mostly been that way historically, and the boers were literally pioneers who had voluntarily broken contact with the Dutch populace due to issues that had lead to mutual alienation.
Because they both had strong feelings about how social conduct should be done, and a strong sense of pride that could only be interpreted as the right to rule, it lead to immense amounts of resentment on both sides, especially when the British started putting afrikaaners in concentration camps. I'm gonna go ahead and say as a South African citizen, that popular claims all those years ago of being the "superior whites" while not savory at all, are as contextually justified as that sort of behavior gets. People don't seem to understand, that the Boers historically were always initially peaceful, they even bought land fairly from the Zulus, but when the tribe changed leaders, the new leader decided he didn't like the whites and wanted to ambush them, the boer settlers never ever forgave the ambush that killed their negotiators, and it turned them into monsters for awhile. That has literally nothing to do with the people alive today, they are different the same way that people in the "Deep American South" are different from the confederates, I don't know where you get your info on modern Afrikaans people.
That being said, nobody who was a male white south african citizen was excluded from the drafts, and they had an effective military. Whether or not their near genocidal shooting incidents were "victories" or "defeats" in terms of casualties the result was the same, foreign nations turned their heads at the release of documentaries detailing the incidents, and decided that small groups of white guys with guns mowing down huge amounts of black people was highly unsavoury, even if there was a part about the huge amounts of black people being the ones who were charging forward in a way that could only be interpreted as violently beforehand. After the international controversy, apartheid had to be put to an end. The people who bring out two dudes with automatic guns to mow down unarmed crowds generally win the battle and lose the war, slicer, you would make a bad general.