Hard Neighbors follows the people who came to be known as Scotch-Irish and traces their relations with Native Americans, examines their experiences as marginalized people, and demonstrates their roles as protective and disruptive forces on the 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 book 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.