As part of the colonization process, African slaves were brought to the island in 1513. Following the decline of the Taíno population, more slaves were brought to Puerto Rico; however, the number of slaves on the island paled in comparison to those in neighboring islands. Also, early in the colonization of Puerto Rico, attempts were made to wrest control of Puerto Rico from Spain. The Caribs, a raiding tribe of the Caribbean, attacked Spanish settlements along the banks of the Daguao and Macao rivers in 1514 and again in 1521 but each time they were easily repelled by the superior Spanish firepower. However, these would not be the last attempts at control of Puerto Rico. The European powers quickly realized the potential of the lands not yet colonized by Europeans and attempted to gain control of them. Nonetheless, Puerto Rico remained a Spanish possession until the 19th century.