In the 1700s a large percentage of all English and American shipping was devoted to moving slaves to the Americas, moving raw goods produced by slaves back to England, and then shipping manufactured items back to Africa and to the Americas.
To capitalized on the wealth generated in the Americas, English authorities utilized an economic and political system known as mercantilism, which viewed colonies as
1) a source of revenue and raw materials,
2) a market for manufactured goods,
3) a way to strengthen a nation's economic self-sufficiency