 That is, indigenous elites inside West and Central Africa made large and growing profits from slavery, thus increasing their wealth and power.Economic historian Stanley Engerman finds that even without subtracting the associated costs of the slave trade (e.g., shipping costs, slave mortality, mortality of British people in Africa, defense costs) or reinvestment of profits back into the slave trade, the total profits from the slave trade and of West Indian plantations amounted to less than 5% of the British economy during any year of the Industrial Revolution.Engerman's 5% figure gives as much as possible in terms of benefit of the doubt to the Williams argument, not solely because it does not take into account the associated costs of the slave trade to Britain, but also because it carries the full-employment assumption from economics and holds the gross value of slave trade profits as a direct contribution to Britain's national income.