importing enslaved Africans for eight years with a maximum of 4,000. Gouvenot promptly sold his licence to the treasurer of the and three subcontractors, Genoese merchants in Andalusia, for 25,000 ducats. The Casa de Contratación in Seville controlled both trade and immigration to the New World, excluding Jews, conversos, Muslims, and foreigners. African slaves were considered merchandise, and their imports were regulated by the crown. The Spanish crown collected a duty on each "pieza", and not on each individual slave delivered. Spain had neither direct access to the African sources of slaves nor the ability to transport them, so the asiento system was a way to ensure a legal supply of Africans to the New World, which brought revenue to the Spanish crown. Portuguese monopoly For the Spanish crown, the asiento was a source of profit. Haring says, "The asiento remained the settled policy of the Spanish government for controlling and profiting from the slave trade." In Habsburg Spain, asientos were a basic method of financing state expenditures: "Borrowing took two forms – long-term debt in the form of perpetual bonds (juros), and short-term loan contracts provided by bankers (asientos). Many asientos were eventually converted or refinanced through juros." Initially, since Portugal had unimpeded rights in West Africa via its 1494 treaty, it dominated the European slave trade of Africans. Before the onset of the official asiento in 1595, when the Spanish monarch also ruled Portugal in the Iberian Union (1580–1640), the Spanish fiscal authorities gave individual asientos to merchants, primarily from Portugal, to bring slaves to the Americas. For the 1560s most of these slaves were obtained in the Upper Guinea area, especially in the Sierra Leone region where there were many wars associated with the Mandé invasions. Following the establishment of the Portuguese colony of Angola in 1575, and the gradual replacement of São Tomé by Brazil as the primary producer of sugar, Angolan interests came to dominate the trade, and it was Portuguese financiers and merchants who obtained the larger-scale, comprehensive asiento that was established in 1595 during the period of the Iberian Union. The asiento was extended to the importation of African slaves to Brazil, with those holding asientos for the Brazilian slave trade often also trading slaves in Spanish America. Spanish America was a major market for African slaves, including many of whom exceeded the quota of the asiento license and were illegally sold. From