In summer 2014, US agencies responsible for the border with Mexico were overwhelmed by tens of thousands of unaccompanied children arriving from Central America. Unprepared to address this unexpected kind of migrant, the US government deployed troops to carry out a new border mission: the feeding, care, and housing of this wave of children.

This event highlights the complex social, economic, and political issues that arise along borders. In American Crossings, nine scholars consider the complicated modern history of borders in the Western Hemisphere, examining borders as...