Who was sold into enslavement after a local or tribal war?

Africans

Explanation:

Generally speaking, we can say that there was domestic slavery in Africa, not commercial slavery, that is, among several African peoples, the slave was not a commodity, but an extra arm in the harvest, livestock, mining and in hunting; one more warrior in the military campaigns.

Beside domestic slavery also existed the slave trade. Some African societies lived on local or tribal warfare to capture people to be sold to other peoples in need of slaves.  As in Africa there were several ethnic groups, many different political groups (Africans were not a single people), the wars between them were very frequent, and one consequence of this was enslavement of the defeated tribe, which could be sold as needed by the winner.