Gabriel joined the faculty of Yale in 1915. Simultaneously, Gabriel was hired as a general editor of
The Pageant of America, an eventual 15-volume series of pictorial history of the development of the United States. In 1931, he collaborated with
Stanley Thomas Williams, an English professor, to teach a course entitled "American Thought and Civilization." He claimed the course "stressed the systematic study of the history of the viewpoints of American writers, scholars, statesmen and reformers." In 1938, Gabriel worked alongside Mabel B. Casner, a Connecticut schoolteacher, to publish
The Rise of American Democracy. A few years later, in 1940, Gabriel published
The course of American democratic thought through the
Ronald Press Company. Although writing as a historian, Gabriel used anthropology to examine how America's "climate of opinion" affected society. He would go on to serve as director of Yale Studies for Returning Service Men from 1944 to 1946 and lecture at the
United States School of Military Government. In 1946, Gabriel founded a new department at Yale, entitled the American Studies Department, and later went on to be a founding father of the
American Studies Association. However, Gabriel would end up resigning from the American Studies Department in protest during the
Cold War. Gabriel was upset that Yale accepted a $500,000 donation on the condition the department focus on "the fundamental principles of American freedom in the field of politics and economics in order to combat the meaning of foreign philosophies". In 1958, Gabriel served as a committee member on the US National Commission for
UNESCO and was a US delegate at the UNESCO conference in Paris. During his lengthy tenure at Yale, Gabriel also served as the editor of the Library of Congress Series in American Civilization. ==Awards and honors==