The comparative approach to the understanding of history is increasingly popular today. This study details the evolution of comparative history by examining the career of a pioneer in this area, Herbert E. Bolton, who popularized the notion that hemispheric history should be considered from pole to pole. Bolton traced the study of the history of the Americas back to 16th century European accounts of efforts to bring civilization to the New World, and he argued that only within this larger context could the histories of individual nations be understood. After American entry into the Spanish-American War in 1898, historians such as Bolton promoted the idea of comparative history, and it remains to this day a significant historiographical approach.Consideration of the history of the Americas as a whole dates back to 16th century European treatises on the New World. Chapter one of this study provides an overview of pre-Bolton formulations of such history. In chapter two one sees the forces that shaped Bolton's thinking and brought about the development of the concept. Chapters three and four focus upon the evolution of the approach through Bolton's history course at the University of California at Berkeley and the reception of the concept among Bolton's contemporaries. Unfortunately, Bolton never fully developed the theoretical side of his arguement; thus, chapter five chronicles the decline of his ideas after his death. The final chapter reveals the survival of the concept, which is now embraced by a new generation of historians who are largely unfamiliar with Bolton's instrumental role in the promotion of comparative history.