By 1650 the kingdoms of Matamba and Portugal had been at war for nearly 25 years, with both sides having become exhausted. Tentative peace talks between Nzingha and the Portuguese began in 1651, would continue in 1654, and would culminate in 1656. The negotiations were aided by Nzingha's recent conversation to Christianity and by the pressure Portugal was facing from its war against Spain. The Portuguese hoped to end the expensive war in Angola and re-open the slave trade, while Nzingha - increasingly cognizant of her age - hoped to have her sister Kambu (often referred to by her Christian name, Barbara, during this period) released. She would not, however, pay the ransom the Portuguese demanded for her sister, and so negotiations repeatedly stalled.