Tensions between Portugal and Kongo increased further as the governors of Portuguese Angola became more aggressive. Luis Mendes de Vasconcelos, who arrived as governor in 1617, used mercenary African groups called Imbangala to make a devastating war on Ndongo, and then to raid and pillage some southern Kongo provinces. He was particularly interested in the province of Kasanze, a marshy region that lay just north of Luanda. Many slaves being deported through Luanda fled into this region and were often granted sanctuary, and for this reason, Mendes de Vasconcelos decided that a determined action was needed to stop it. The next governor of Angola, , used the Imbangala to launch a full-scale invasion of southern Kongo in 1622, following the death of Álvaro III. Correia de Sousa claimed he had the right to choose the king of Kongo. He was also upset that the Kongolese electors chose Pedro II, a former Duke of Mbamba. Pedro II was originally from the duchy of Nsundi, hence the name of the royal house he created, the House of Nsundi. Correia de Sousa also contended that Pedro II had sheltered runaway slaves from Angola during the latter's governorship of Mbamba.