Solution:Bordeaux and Nantes owed their economic prosperity to the flourishing slave trade.
A slave trade emerged in the 17th century between Europe, Africa and the Americas. The reason for this was the need for a vast workforce to work in the French colonies in the Caribbean to produce essential commodities like tobacco, indigo, sugar and coffee. The French sailors left for the African coast from the ports of Bordeaux and Nantes and purchased enslaved people from the local chieftains. They delivered them across the Atlantic Ocean to the Caribbean colonies of Martinique, Guadeloupe, and San Domingo to be sold to the plantation owners. The port cities of Nantes and Bordeaux became economically prosperous because of this flourishing slave trade.