Angolan dominance of the trade was pronounced after 1615 when the governors of Angola, starting with Bento Banha Cardoso, made alliance with Imbangala mercenaries to wreak havoc on the local African powers. Many of these governors also held the contract of Angola as well as the asiento, thus insuring their interests. Shipping registers from Vera Cruz and Cartagena show that as many as 85% of the slaves arriving in Spanish ports were from Angola, brought by Portuguese ships. In 1637 the Dutch West India Company employed Portuguese merchants in the trade. The earlier asiento period came to an end in 1640 when Portugal revolted against Spain, though even then the Portuguese continued to supply Spanish colonies.