During World War I, he served at the rank of captain in the United States Military Intelligence Division of the General Staff from 1918 to 1919. Nine years later, under the direction of General Connor, the head of the War Department, he was asked to serve on an advisory committee of historians to organize documents pertaining to the American participation in the fighting in France. This earned him the title of major. In the 1930s, he was a member of the Catholic Association for International Peace. He served a term as president of the American Historical Association in 1945 and was head of the New York State Historical Association in Cooperstown. He was also a member of the American Philosophical Society.