When European demand for the products from the Spanish Main and the Caribbean Islands soared in the 17th and 18th centuries, a very profitable system was set up to transport these goods back to England, Spain, France and The Netherlands. The so called Triangular Trade took manufactured products such as cloth, iron and beer to Africa to be exchanged for slaves, which were then takes across the Atlantic and sold at tremendous profit. The ships then loaded up with sugar, molasses and rum and headed back to Europe in a triangular circuit that took about a year to complete.
By the beginning of the 18th century all of this wealth, the slave ships coming in from Africa and the goods laden ships leaving for Europe, had become irresistible targets for looters and pirates. The golden age of piracy was born, not due to grand efforts on the part of the pirates themselves, but because of the abundance of spoils and the ease of taking them.
Here’s some more reading material: http://piratesoflore.com/triangular-trade.html