Tolong jelaskan mengenai Karya dari Nicholas J. Spykman

The Geography of the Peace, New York, Harcourt, Brace and Company (1944)

America's Strategy in World Politics: The United States and the Balance of Power, New York, Harcourt, Brace and Company (1942)

The Social Theory of Georg Simmel, Chicago, University of Chicago Press (c1925)