Initially, the Kongo people exchanged ivory and copper objects they made with luxury goods of Portuguese. But, after 1500, the Portuguese had little demand for ivory and copper, they instead demanded slaves in exchange. The settled Portuguese in São Tomé needed slave labor for their sugarcane plantations, and they first purchased labor. Soon thereafter they began kidnapping people from the Kongo society and after 1514, they provoked military campaigns in nearby African regions to get slave labor. Along with this change in Portuguese-Kongo people relationship, the succession system within Kongo kingdom changed under Portuguese influence, and in 1509, instead of the usual election among the nobles, a hereditary European-style succession led to the African king Afonso I succeeding his father, now named João I. The slave capture and the export of slaves caused major social disorder among the Kongo people, and the Kongo king Afonso I wrote letters to the king of Portugal protesting this practice. Finally, he succumbed to the demand and accepted an export of those who willing accepted slavery, and for a fee per slave. The Portuguese procured 2,000 to 3,000 slaves per year for a few years, from 1520, a practice that started the slave export history of the Kongo people. However, this supply was far short of the demand for slaves and the money slave owners were willing to pay.