Leo XIII was one of the great popes of the modern era. He won for the papacy renewed international authority after a long period of declining prestige. Like his predecessors, he attacked socialism, communism, nihilism, and freemasonry, but not simply in a manner that was intellectually and politically reactive. Rather, Leo’s opposition to these forces led him to develop a program of qualified accommodation with the modern world. This program defined the different spheres of temporal and spiritual power, gave qualified approval to democracy, and put forward the claim that the Church is not an opponent but, rather, the true custodian of liberty, properly understood.