Why did the people hate Twala in King Soloman's Mines?

In the classic adventure novel King Solomon's Mines by H. Rider Haggard, Allen Quartermain and his expedition travel deep into Africa in search of the lost treasure of King Solomon. After traversing a desert and a range of mountains, they come into a valley called Kukuanaland.

Twala has become the king of the Kukuanas by murdering his brother, the previous king. He is hated by the people because he is a cruel man. When the travelers meet him, Quartermain reports that he has "the most repulsive countenance we had ever beheld." He has only one eye, and the other eye socket is hollow. "His whole expression was cruel and sensual to a degree." Twala immediately demonstrates his cruelty by having one of his warriors thrust through with a spear merely for accidentally dropping his shield. Later, one of the people says,

The land groans at the cruelties of Twala the king; it is weary of him and his red ways.

As an advisor, Twala keeps a very old woman named Gagool. They conduct regular witch hunts and murder without trial any opponents of King Twala. Eventually there is a rebellion in which the Englishmen assist, and Twala is overthrown and beheaded.