Machiavellianism is named after 16th century political strategist Niccolo Machiavelli. He wrote a book titled Il Principe where he advised rulers with a clear agenda to secure their power through careful planning, and if necessary, cruel and unethical means (e.g. executing political rivals). These rulers should be open to any and all effective tactics, including manipulative interpersonal strategies such as flattery and lying. Psychologists in the 1960s observed the parallels between Machiavelli's political strategies and people's everyday social behavior and later grouped these similarities as a personality trait by the name of "Machiavellianism."