Bemis joined the faculty at George Washington University in 1924, remaining there a decade, and accepted the history department's chairmanship in 1925.
His presidential address for the AHA engaged the topic of "American Foreign Policy and the Blessings of Liberty".
It has been a failure, not because the United States did not join it; but because the great powers have been unwilling to apply sanctions except where it suited their individual national interests to do so, and because Democracy, on which the original concepts of the League rested for support, has collapsed over half the world.
His tone was nationalistic, typically blaming America's antagonists for conflicts, but he rose above jingoism and provided analysis which ran counter to State Department views.
For Bemis, the great achievement US–Latin American relations was Franklin Roosevelt's Good Neighbor policy.
Bemis's books include Jay's Treaty: A Study in Commerce and Diplomacy (1924 and later reprint editions), which won the Knights of Columbus Historical Prize.
His 18-volume series The American Secretaries of State and Their Diplomacy appeared first in ten volumes (published by Knopf in 1927–1929) covering Robert R. Livingston to Charles Evans Hughes.
These were reprinted in 1958, and the success of the series prompted the creation of a further eight volumes, covering Frank B. Kellogg to Christian Herter, published through 1972.