The American Indian as Participant in the Civil War is a meticulous historical study of Native nations drawn into the sectional conflict, especially in the trans-Mississippi West and Indian Territory. Abel traces diplomacy, military service, divided loyalties, and the devastating consequences of alliance with Union and Confederate powers. Written in a documentary, analytical style characteristic of early twentieth-century professional history, the book situates Indigenous agency within Civil War historiography that too often confined the war to eastern battlefields. Annie Heloise Abel, a pioneering historian of Native American and western history, brought rigorous archival training to subjects then neglected by mainstream scholarship. Educated in an era when few women entered the historical profession, she developed a sustained interest in federal Indian policy, frontier administration, and wartime diplomacy. Her attention to treaties, official correspondence, and political motives reflects both her scholarly method and her desire to recover Indigenous presence in national narratives. This book is recommended for readers seeking a fuller understanding of the Civil War's geographic and moral scope. Though shaped by the terminology and assumptions of its time, it remains valuable for its evidentiary richness and insistence that Native peoples were not peripheral observers but active, consequential participants in the conflict.