How did the slave trade affect Africa's political structures?

The majority of the African slave trade consisted of
Europeans trading African tribes for slaves. The slave trade became so lucrative for
Africans themselves that they frequently waged war against other tribes in an attempt to
secure captives for the trade. Among those kingdoms who profited from the slave trade
was the kingdom of Ndongo, which Portuguese traders referred to as Angola, after the
title of the Ndongo King. Portuguese slaving efforts were opposed by a powerful Queen,
Nzinga, who dressed as a man and insisted her subjects refer to her as the King. On one
occasion, when she met with the Portuguese governor of Angola and he refused to offer
her a chair, she sat on the back of her servant while she negotiated with him.