Hard Neighbors highlights stories that have been subsumed by terms such as "English settlers" and "American expansion" and traces shifting relationships involving Scotch-Irish people living on the frontier, neighboring Indian peoples, and more distant governments. It follows the people who came to be known as Scotch-Irish from their genesis on a colonial borderland on one side of the Atlantic to their role in the borderlands of Indian country on the other. It traces their relations with Native Americans over time and across the continent, examines their experiences as marginalized and expendable people living between colonial powers and Indigenous peoples, and demonstrates their roles as protective and disruptive forces on the hard edge of colonialism. The Scotch-Irish fought Indian wars and shaped the frontier, and their experiences living near and fighting against Indians shaped their identity and their attitudes towards government. They influenced national attitudes and policies, and they transformed Indian people into racial others as they transformed themselves into Americans.

The story this book tells is less about the Scotch-Irish as a distinct ethnic group than as a people in motion who, in collusion and conflict with colonial authorities, repeatedly inserted themselves on Native land. Instead of a tale of unified westward expansion, it recovers the experiences, encounters, and humanity of groups of people enmeshed in the violence of colonialism and reconstructs the roles of multiple peoples placed as buffers between competing powers. Expansion, and the accompanying expulsion and killing of Indian people, helped to create American unity and identity and, ultimately, made the Scotch-Irish Americans. Once marginalized as little better than Indians, they reaffirmed their reputation as Indian killers and made a place for themselves in America, as Americans.