His father, Col. Robert L. Thornton, was then serving in the US Air Force, eventually becoming a professor of Business Administration at Miami University in Oxford, Ohio.
However, he argued, the persistent civil wars of the seventeenth century and the rise of a new population center in the coastal province of Soyo led to the depopulation of São Salvador and the loss of its centralization.
In 2007 he and his longtime collaborator (and wife) Linda Heywood published Central Africans, Atlantic Creoles and the Foundation of the Americas, 1585–1660 (Cambridge University Press).
This work demonstrated that thanks to English and Dutch privateering on Portuguese vessels, virtually all the first generation of slaves brought to the colonies of these two countries came from Central Africa.
They then went on to argue that the long contact between this region and Europe, the conversion of many of the people to Christianity, and the adaptation of various European items of culture, they could be considered "Atlantic Creoles" a term popularized by historian Ira Berlin.
Basing themselves of many local archives in the United States, Bermuda, Barbados, England and the Netherlands, they went on to suggest that the Christian background of many early slaves may account for their high manumission rate and their role in cultural foundations of the Americas.
He shared the 2008 Herskovits Prize for his book (co-authored with Linda Heywood) Central Africans, Atlantic Creoles, and the Foundation of the Americas, 1585–1660.