There has been a long-standing debate on the global importance of the African external slave trades. While many scholars believe these to have been detrimental to African development, they were clearly a determining factor in the development of the Americas. What role they played for the European colonial powers is, however, hotly debated. This article contributes to the debate by estimating value added in the Triangular Trade and the American plantation complex. The article empirically studies the case of British connections to the African slave trade and the American plantation complex during the eighteenth century, since these have been the focus of much previous scholarly debate. The estimates suggest that these trades grew substantially over the period, reaching a magnitude equivalent to about 11% of the British economy by the early nineteenth century.