The most compelling argument for including international relations within political science is that its focus and core principles are found in the dominant concerns of political science.

Until the late 1930's, approaches to the study of international relations were those of diplomatic history, international law or current events. History for a time had a monopoly on the study of international relations and the classic works of Harold Nicolson, Webster, Mowat and Butterfield were the centerpieces of the subject. Diplomatic history was a branch of historical studies and its rigor and systematic approach earned the admiration of university leaders.

International law completed with diplomatic history and added a new dimension of hope for change and reform.