The most essential new development that sets in modern political theory apart from the past is the new discipline of political science. Plato’s ideas emerged from his fertile mind. Medieval kings ruled by fiat with very little feedback about how they were doing. Modern political science looks at what actually happens and tries to explain it and asses how well it works.

Of the many influences on American political theory, none is more essential that John Locke’s Second Treatise on Civil Government. The American founders were well read in all philosophy. And they certainly gave attention to many thinkers. But where the others contributed fragments, Locke’s ideas account for the major structure of America’s government.

The Prince contains, for almost the first time anywhere, an interest in the feelings and wishes of ordinary people. Machiavelli doesn’t mean to balance the rights of citizens against the rights of rulers. He just means to remind Medici that the citizens have feelings and motivations of their own, and that ruling them is easier when those wishes are considered.

Medieval rulers could do, within their own territory, what seemed best to his own mind. That worked well when the man was good, and worked badly when the man was weak or wicked. There were very few rules or constraints on medieval kings. And yet, when the barons sat down at Runnymede in 1215 to list what seemed proper, they produced ideas that inspired America’s founders in 1787.

“[W]e need in these present circumstances to be brave men and not give up but try—if ever we are able—to save ourselves by conquering nobly, and if we are not, let us at least die nobly!”