Protestantism also spread from the German lands into France, where the Protestants were nicknamed Huguenots. Calvin continued to take an interest in the French religious affairs from his base in Geneva. He regularly trained pastors to lead congregations there. Despite heavy persecution, the Reformed tradition made steady progress across large sections of the nation, appealing to people alienated by the obduracy and the complacency of the Catholic establishment. French Protestantism came to acquire a distinctly political character, made all the more obvious by the conversions of nobles during the 1550s. This established the preconditions for a series of conflicts, known as the French Wars of Religion. The civil wars gained impetus with the sudden death of Henry II of France in 1559. Atrocity and outrage became the defining characteristics of the time, illustrated at their most intense in the St. Bartholomew's Day massacre of August 1572, when the Roman Catholic party annihilated between 30,000 and 100,000 Huguenots across France. The wars only concluded when Henry IV of France issued the Edict of Nantes, promising official toleration of the Protestant minority, but under highly restricted conditions. Roman Catholicism remained the official state religion, and the fortunes of French Protestants gradually declined over the next century, culminating in Louis XIV's Edict of Fontainebleau which revoked the Edict of Nantes and made Roman Catholicism the sole legal religion once again. In response to the Edict of Fontainebleau, Frederick William I, Elector of Brandenburg declared the Edict of Potsdam, giving free passage to Huguenot refugees. In the late 17th century many Huguenots fled to England, the Netherlands, Prussia, Switzerland, and the English and Dutch overseas colonies. A significant community in France remained in the Cévennes region.