Professor Sparrow studies American political development and the conjunction between the American state and the international system. His current research is on impact of the immigration of indentured servants to the American colonies in the seventeenth and eighteenth centuries.  He also, and relatedly, studies American territorial policies from the 18th to the 21st centuries, from the trans-Appalachian west in the eighteenth century, to Puerto Rico, Guam, and the Northern Marianas at present.