White, The Republic for Which It Stands, 799–800.

Walter Lippmann, Drift and Mastery (New York: Mitchell Kennerley, 1914), 80–81.

Robert Margo, "The Labor Force in the Nineteenth Century", The Long Nineteenth Century, vol. 2 of The Cambridge Economic History of the United States, ed. Stanley Engerman and Robert Gallman (Cambridge: Cambridge University Press, 2000), 238.