in 1621 the Dutch West India Company was chartered to take them over.  Closely identified with the Dutch government, this company not only founded the colony of New Netherland and endeavored to foster the employment of negro slaves there, but in 1634 it seized the Spanish island of Curacao near the Venezuelan coast and made it a basis for smuggling slaves into the Spanish dominions.  And now the English, the French and the Danes began to give systematic attention to the African and West Indian opportunities, whether in the form of buccaneering, slave trading or colonization.

The revolt of Portugal in 1640 brought a turning point.  For a quarter-century thereafter the Spanish government, regarding the Portuguese as rebels, suspended all trade relations with them, the asiento included.  But the trade alternatives remaining were all distasteful to Spain.  The English were heretics; the Dutch were both heretics and rebels; the French and the Danes were too weak at sea to handle the great slave trading contract with security; and Spain had no means of her own for large scale commerce.  The upshot was that the carriage of slaves to the Spanish colonies was wholly interdicted during the two middle decades of the century.  But this gave the smugglers their highest opportunity.  The Spanish colonial police collapsed under the pressure of the public demand for slaves, and illicit trading became so general and open as to be pseudo legitimate.  Such a boom came as was never felt before under Protestant flags in tropical waters.  The French, in spite of great exertions, were not yet able to rival the Dutch and English.  These in fact had such an ascendency that when in 1663 Spain revived the asiento by a contract with two Genoese, the contractors must needs procure their slaves by arrangement with Dutch and English who delivered them at Curacao and Jamaica.  Soon after this contract expired the asiento itself was converted from an item of Spanish internal policy into a shuttlecock of international politics.  It became in fact the badge of maritime supremacy, possessed now by the Dutch, now by the French in the greatest years of Louis XIV, and finally by the English as a trophy in the treaty of Utrecht.

By this time, however, the Spanish dominions were losing their primacy as slave markets.  Jamaica, Barbados and other Windward Islands under the English; Hayti, Martinique and Guadeloupe under the French, and Guiana under the Dutch were all more or less thriving as plantation colonies, while Brazil, Virginia, Maryland and the newly founded Carolina were beginning to demonstrate that slave labor had an effective calling without as well as within the Caribbean latitudes.  The closing decades of the seventeenth century were introducing the heyday of the slave trade, and the English were preparing for their final ascendency therein.