I know this is kind of farfetched, but...
Could the Zulu, led by Shaka, conquer all of South Africa? They did manage to rule a number of local tribes, but they never went across the Tugela river or over the Drakensberg Mountains, where they might have come into contact with the Xhosa or the Boers.
Could they have plausibly defeated them? If Shaka did manage to overpower the Xhosa, would he have been able to secure a permanent foothold(maybe limiting Boer expansion)in South Africa? Or, and this is a little out there, could he have managed to secure British help/guns/horses to defeat the Voortrekkers when they set out on the Great Trek?
I'm newbie here, but some suggestions on this would really help, because I'm thinking of making an ATL of the Great Trek and Shaka's empire.