23 On the other hand, the doctrines on political power invented by late writers have already produced great ills amongst men, and it is to be feared that they will cause the very greatest disasters to posterity. For an unwillingness to attribute the right of ruling to God, as its Author, is not less than a willingness to blot out the greatest splendor of political power and to destroy its force. And they who say that this power depends on the will of the people err in opinion first of all; then they place authority on too weak and unstable a foundation. For the popular passions, incited and goaded on by these opinions, will break out more insolently; and, with great harm to the common weal, descend headlong by an easy and smooth road to revolts and to open sedition. In truth, sudden uprisings and the boldest rebellions immediately followed in Germany the so-called Reformation,(29) the authors and leaders of which, by their new doctrines, attacked at the very foundation religious and civil authority; and this with so fearful an outburst of civil war and with such slaughter that there was scarcely any place free from tumult and bloodshed. From this heresy there arose in the last century a false philosophy - a new right as it is called, and a popular authority, together with an unbridled license which many regard as the only true liberty. Hence we have reached the limit of horrors, to wit, communism, socialism, nihilism, hideous deformities of the civil society of men and almost its ruin. And yet too many attempt to enlarge the scope of these evils, and under the pretext of helping the multitude, already have fanned no small flames of misery. The things we thus mention are neither unknown nor very remote from us.
Source: Diuturnum (Vatican.va)