Casualties/war/violence did not start with the arrival of the Dutch as you are implying. Casualties/war/violence is part of human nature. For example there is clear evidence that the Bantus violently drove the Khoisan out of much of South Africa some 4000 years ago.

The long term trend is however that South Africa (and the rest of the world) is become less violent and more humane. For example slavery was abolished here in 1834.