French Protestantism, though its appeal increased under persecution, came to acquire a distinctly political character, made all the more obvious by the noble conversions of the 1550s. This had the effect of creating the preconditions for a series of destructive and intermittent conflicts, known as the Wars of Religion. The civil wars were helped along by the sudden death of Henry II in 1559, which saw the beginning of a prolonged period of weakness for the French crown. and outrage became the defining characteristic of the time, illustrated at its most intense in the St. Bartholomew's Day massacre of August 1572, when the Catholic Church annihilated between 30,000 and 100,000 Huguenots across France. The wars only concluded when Henry IV, himself a former Huguenot, issued the Edict of Nantes, promising official toleration of the Protestant minority, but under highly restricted conditions. 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 Catholicism the sole legal religion of France. In response to the Edict of Fontainebleau, Frederick William of Brandenburg declared the Edict of Potsdam, giving free passage to French Huguenot refugees, and tax-free status to them for 10 years.