In the 1550s, the establishment of the Geneva church provided leadership to the disorganized French Calvinist (Huguenot) church. The French intensified the fight against heresy in the 1540s forcing Protestants to gather secretly to worship. But by the middle of the century, the adherents to Protestantism in France had increased markedly in number and power, as the nobility in particular converted to Calvinism. Historians estimate that in the 1560s more than half of the nobility were Calvinist (or Huguenot), and 1,200–1,250 Calvinist churches had been established; by the outbreak of war in 1562, there were perhaps two million Calvinists in France. The conversion of the nobility constituted a substantial threat to the monarchy. Calvinism proved attractive to people from across the social hierarchy and occupational divides, and it was highly regionalized, with no coherent pattern of geographical spread.