feb 11, 1532 - Machiavelli, The Prince
The Prince explained the thought process that a leader must contain in order to rule his nation and to conquer others, which the traits are that of a person so focused on their own interests they will manipulate, deceive, and exploit others to achieve their goals. In the book, Machiavelli was able to form a new perspective on the nature of leaders, retaining from simple facts into the darker part of psychological tendencies that are needed to succeed, which relate back to the AP them (OS).
Added to timeline:
AP Euro Timeline - Metelski