What was the name of book published in early 16th century that is famous for asserting a leader should be both loved and feared but it safer to than loved?

The book you're referring to is The Prince, written by Niccolò Machiavelli and published in 1532.

While the book was not actually published in the early 16th century (it was published later), the ideas it contained were circulated and discussed throughout the 16th century.

Machiavelli's famous quote from the book is: "It is better to be feared than loved, if you cannot be both." He argued that a leader should prioritize maintaining power and security, even if it means using fear to control the population.