In 1521, the Catholic Church declared war on Martin Luther. The German monk had already been excommunicated the year before, after nailing his Ninety-Five Theses -- which accused the Church of rampant corruption -- to the door of a Saxon church. Now, the Holy Roman Emperor Charles V called for Luther "to be apprehended and punished as a notorious heretic." The edict was akin to a death sentence: If Luther was caught, he would almost inevitably be...