Donald Trump learned his trade doing real estate deals in New York long before he ever ran for office, and the lesson he carried into the Oval Office was simple: whoever needs the deal less controls the table. In his 1987 book on dealmaking, he described leverage as having something the other side wants, or better, something it cannot do without. Almost forty years later, that instinct still drives his foreign policy and his trade fights. He does not negotiate the way career diplomats do, by working slowly toward consensus. He disrupts the baseline first and lets the discomfort do the negotiating for him.

The Greenland security pact he signed on September 22 is the clearest recent example.

It’s a good bet that most Americans have never heard of Nicholas Spykman. He was born on October 13, 1893, in Amsterdam, the Netherlands. He attended Delft University and during the First World War served in Dutch diplomatic posts in Cairo and the Dutch East Indies. In 1920, he came to the United States, and three years later earned his Ph.D. at the University of California, writing about the theories of the sociologist Georg Simmel. His first book, The Social Theory of Georg Simmel, was published by the University of Chicago Press in 1925. That same year, he joined the faculty of Yale University, where in 1928 he became a professor of international relations. In the 1930s, he headed Yale’s Institute of International Studies, and in the lead-up to the Second World War wrote two articles for the American Political Science Review on the relationship of geography to American national security. Those articles formed the basis of his most important book, America’s Strategy in World Politics: The United States and the Balance of Power (1942).

Hans Morgenthau is generally considered to be the “father” of foreign policy realism in the United States based on his 1949 book Politics Among Nations: The Struggle for Power and Peace, though the American diplomat and historian George F. Kennan claimed that Reinhold Niebuhr, the author of Moral Man and Immoral Society, deserved that honor. Nicholas Spykman can be called the godfather of American foreign policy realism. America’s Strategy in World Politics and his second book on geopolitics, The Geography of the Peace (published posthumously in 1944—Spykman died in 1943), are still worth reading today for their insights on the nature of international politics.