In 1667, he sent his ambassador, Anastasius, to Luanda (Angola), to negotiate a treaty that ceded to the Portugueses the right to exploit the mines of Congo, located in the provinces of Mbamba and Mpemba. Theodosius, Duke of Mbamba, bowed to the king's decision, but Pedro III of Kongo, refused.
Leading a small army, Peter attacked Mbamba, killed Theodosius and then invaded the kingdom's capital, São Salvador, killing Alvaro VIII and proclaimed himself king under the name of Peter III.