The document discusses the Protestant Reformation and the Catholic Counter-Reformation that occurred in 16th century Europe. It began with Martin Luther challenging the Catholic Church's sale of indulgences in 1517, which led to the spread of Protestant doctrines like Lutheranism. In response, the Catholic Church enacted reforms through the Council of Trent and the Society of Jesus to reaffirm Catholic doctrine and train priests to spread the faith. These religious changes fractured the unity of the Catholic Church and altered the course of Christianity in Western Europe.