In "Frontier Country," Patrick Spero addresses one of the most important and controversial subjects in American history: the frontier. Countering the modern conception of the American frontier as an area of expansion, Spero employs the eighteenth-century meaning of the term to show how colonists understood it as a vulnerable, militarized boundary. The Pennsylvania frontier, Spero argues, was constituted through conflicts not only between colonists and Native Americans but also among neighboring British colonies. These violent encounters created what Spero describes as a distinctive "frontier society" on the eve of the American Revolution that transformed the once-peaceful colony of Pennsylvania into a "frontier country."