Final answer:
The two biggest rival tribes in South Africa were the Zulu and the Xhosa, both of which were major indigenous groups that significantly influenced the country's history and cultural landscape.
Step-by-step explanation:
The two dominant or biggest rival tribes in South Africa were the Zulu and the Xhosa. These indigenous ethnic groups played a significant role in the country's history. The Zulu, led by their formidable leader Shaka Zulu, established a powerful kingdom and successfully resisted European colonization for a time. The Xhosa, known for their farming and resistance to colonial intrusion, engaged in a series of wars, particularly with the Dutch settlers. Both these groups have been instrumental in shaping the cultural and historical landscape of South Africa.