The Kingdom of Kongo was a large, centralized Central African state near the mouth of the Congo River, ruled by the manikongo from the capital Mbanza Kongo. Its kings adopted Christianity of their own will after 1483 and corresponded as equals with Portugal and the Pope, even as the same Atlantic link drew the kingdom into a slave trade that hollowed it out over the following centuries.
Around 1526, a Christian king in Central Africa wrote to the king of Portugal to protest a slave trade that had escaped his control. Afonso I of Kongo complained that Portuguese merchants and their allies were seizing free Kongolese people — even nobles and members of his own family — and shipping them across the sea. He wrote as a fellow Catholic monarch, in fluent Portuguese, citing their shared faith. He did not reject slavery itself; his world accepted captive labor. What he protested was illegal enslavement and the loss of royal control. The trade deepened anyway, feeding factional war and Portuguese pressure for centuries. Kongo is the rare case where a ruler caught inside the Atlantic system left a written record, in his own royal voice, of trying to rein it in.