Professor Onuf is a nationally renowned Jefferson scholar, and has written extensively on sectionalism, federalism, and political economy, with a particular emphasis on the political thought of Thomas Jefferson. Most recently, with his brother, political theorist Nicholas G. Onuf, he collaborated on Nations, Markets, and War: Modern History and the American Civil War (2006), a history of international law and order in the Atlantic states' system during the Age of Revolutions and early nineteenth century, and a collection of his essays, The Mind of Thomas Jefferson (2007)