Much of the conflict Hostile_encounter took place Hold during the long regency of Queen Catherine de ' Medici , widow of Henry II of France , for her minor sons .

A most notable moderate , at least initially , was the queen mother , Catherine de ' Medici .

A large Imperial and Spanish army under Philibert of Châlon , Prince of Orange and Pier Maria III de ' Rossi surrounded Surrounding the city , and , after a siege of nearly ten months , captured Conquering it , overthrowing Change_of_leadership the Republic of Florence and installing Placing Alessandro de ' Medici as the ruler of the city .

The Florentines had thrown off GiveUp Medici rule and established Building a republic after the Sack of Rome in 1527 ; the Florentine Republic had continued to participate Participation in the war on the side of the French .

Charles , attempting to gain Clement 's favor , ordered Arranging his armies to seize Florence and return Arriving the Medici to power .