Start of the Wars of Religion, the massacre of Wassy
The massacre, on March 1st, by the Duke de Guise’s troops of some hundred Protestants attending religious services in a barn located inside the ramparts of the city of Wassy (Champagne) and not outside as stipulated by the Edict of January 1562, is considered the event that triggered the first War of Religion.
Article : The massacre of Wassy (1562)