In 1520 the Florentine merchants again had recourse to Machiavelli to settle their difficulties with Lucca, but this year was chiefly remarkable for his re-entry into Florentine literary society, where he was much sought after, and also for the production of his “Art of War.” It was in the same year that he received a commission at the instance of
Cardinal de’ Medici to write the “History of Florence,” a task which occupied him until 1525. His return to popular favour may have determined the Medici to give him this employment, for an old writer observes that “an able statesman out of work, like a huge whale, will endeavour to overturn the ship unless he has an empty cask to play with.” - The Prince, Niccolo Machiavelli
On the death of Pius III, in 1503, Machiavelli was sent to Rome to watch the election of his successor, and there he saw Cesare Borgia cheated into allowing the choice of the College to fall on Giuliano delle Rovere (Julius II), who was one of the cardinals that had most reason to fear the duke. Machiavelli, when commenting on this election, says that he who thinks new favours will cause great personages to forget old injuries deceives himself. Julius did not rest until he had ruined Cesare. - The Prince, Niccili Machiavelli