In what historical period is The Prince set?
Machiavelli's The Prince is set presumably during his own lifetime (1469-1527). Machiavelli does provide the reader with a number of clues to suggest this. Two of his favorite examples, Francesco Sforza and Cesare Borgia, as well as other figures such as Alexander VI and Ferdinand of Aragon, lived during Machiavelli's lifetime. Keeping in mind Machiavelli's intention to provide an instruction book for a ruler who could survive the ruthlessness of sixteenth-century Italian (read Florentine) politics, the advice he gives is in many ways specific to his own time.
The Prince, by Machiavelli, is based on the career of Cesare Borgia, an Italian nobleman who lived ca. 1475-1507, during the Italian Renaissance. Machiavelli greatly admired Borgia and with The Prince encouraged other noblemen to follow his style of leadership. See the enotes article at the attached link.