aug 24, 1572 - St. Bartholomew's Day Massacre
French Catholics attacked French Huguenots in Paris during the marriage of Margaret of Valois to the Protestant Henry of Navarre, which was intended to reconcile the Protestants. Calvinist Admiral Gaspard de Coligny, who had been advising Charles IX, was also there, and Catherine de Medici tried to have him assassinated by Henry of Guise the night before. Henry of Guise and the Guise family in general were seen as major threats to the Empire. Charles IX's inconsistent and indecisive rules escalated the conflict further.
Added to timeline: