Final answer:
The conflict between Queen Nzinga and the Portuguese was primarily caused by her resistance to their attempts to expand their control into her kingdom. Nzinga's alliance with the Dutch and her support of the slave trade also contributed to the conflict.
Step-by-step explanation:
The primary cause of conflict between Queen Nzinga and the Portuguese was her resistance to their attempts to expand their control into her kingdom. Portugal reneged on the terms of a treaty and demanded that Ndongo become a vassal state.
In addition to her resistance, Nzinga's alliance with the Dutch posed a threat to the Portuguese. The Portuguese also opposed Nzinga's support of the slave trade, as they sought to control it.
Ultimately Nzinga concluded a peace treaty with Portugal in 1656, ending the hostilities.