in 1572, the fourth war broke out when the catholics, led by henry of valois and henry of guise, the son of duke francis, who was killed during the first war, killed coligny and thousands of other protestants during the saint bartholomew's day massacre. many protestant survivors fled to la rochelle, one of the main centres of protestantism in france. the catholic army put la rochelle under siege but could not conquer the city. after losing thousands of soldiers, the catholics agreed to a peace treaty. between the fourth and the fifth wars, king charles ix died, and his younger brother, henry, became king henry iii.