An excerpt from ‘Capitalism and Slavery’ by Eric Williams, chapter 3 ‘Commerce and the triangular trade’:
In this triangular trade England – France and Colonial America equally – supplied the exports and the ships; Africa the human merchandise; the plantations the colonial raw materials. The slave ship sailed from the home country with a cargo of manufactured goods. These were exchanged at a profit on the coast of Africa for Negroes, who were traded on the plantations, at another profit, in exchange for a cargo of colonial produce to be taken back to the home country. As the volume of trade increased, the triangular trade was supplemented, but never supplanted, by a direct trade between the home country and the West Indies (the Caribbean), exchanging home manufactures directly for colonial produce.
The triangular trade thereby gave a triple stimulus to British industry. The Negroes were purchased with British manufactures; transported to the plantations, they produced sugar, cotton, indigo, molasses and other tropical products, the processing of which created new industries in England; while the maintenance of the Negroes and their owners on the plantations provided a new market for British industry, New England agriculture and the Newfoundland fisheries. By 1750 there was hardly a trading or a manufacturing town in England which was not in some way connected with the triangular or direct colonial trade. The profits obtained provided one of the main streams of that accumulation of capital in England which financed the Industrial Revolution.