The Spanish established sugar and tobacco as Cuba's primary products, and the island soon supplanted Hispaniola as the prime Spanish base in the Caribbean. Further field labor was required. African slaves were then imported to work the plantations as field labor. However, restrictive Spanish trade laws made it difficult for Cubans to keep up with the 17th and 18th century advances in processing sugar cane pioneered in Barbados, Jamaica and Saint-Domingue. Spain also restricted Cuba's access to the slave trade, instead issuing foreign merchants "asientos" to conduct it on Spain's behalf. The advances in the system of sugar cane refinement did not reach Cuba until the Haitian Revolution in the nearby French colony of Saint-Domingue led to thousands of refugee French planters to flee to Cuba and other islands in the West Indies, bringing their slaves and expertise in sugar refining and coffee growing into eastern Cuba in the 1790s and early 19th century.