 Johnson spent the years 1895 to 1897 studying history in Europe, with three semesters at the University of Leipzig (under Karl Gotthard Lamprecht and ), and one semester in Paris at the École Libre des Sciences Politiques.Johnson then finished his Ph.D. at Columbia University under James Harvey Robinson, with a dissertation entitled "The Intendant as a Political Agent under Louis XIV" (1899).Johnson began teaching history at Iowa College (now Grinnell College) in 1898.