Asiento was a liscense issued by Spain to provide slave to its colonies. The Treaty of Tordesillas in 1494 separated Spain from African source of slaves. It issued liscences to  provide slaves to its colonies. The Portuguese initially owned the asiento, later the Dutch, the French, a Genoese Company, and then the English. For a period of time, between 1750-1862, Spain issued it to herself. This liscence was lucrative to the nation that owned it. Many European nation competed among each other for it.