Huh? Monarchical societies have been the dominant form of government for centuries, and even the Papacy, in its secular aspect, is a monarchy.
What the Holy Father is arguing, in my opinion, is that Christianity is the staple of the modern democratic diet that makes it (modern democracies) work. It’s the filler between the cracks, the mortar that holds the superfices together. The democracies of antiquity were highly unstable, bloody, aggressive, brutal, and prone to actively persecuting their own people (and this even before many of them became Christians), etc. They paid little regard to any value inherent in or to human life, if such a notion even existed then as it does today (I don’t believe it did at all).
Monarchies, even benevolent ones, hardly have encouraged democracy.
Some did (and do) encourage democracy, but certainly owing to political expediency more than for, shall we say, humanitarian reasons (e.g., the British monarchy). Most openly condemned democracy as a seed of anarchy, division and faction, among other reasons (e.g., Spain, Russia, France, I think also Austria-Hungary would have). Many also condemned liberalism in general, if I recall. These ideas seriously threatened the prevalent social order and did that for the sake of a what was then only a theory. Today, we hardly pay any attention to anyone who would radically alter or topple the social order for the sake of a theory, but if it became popular we might care to listen or learn about it. Now, depending upon our conclusions, we might strongly support or strongly resist that theory, praise it or condemn it.
Pax,
Tim