Events like the one in France in 1789, or in Russia in 1917, etc. happen from time to time. And sociologists still do not know why. There are several conflicting theories, but nobody knows why exactly, and how to prevent it. Louis XVI, the king of France, even wrote in his diary on July 14, 1789: "Rien", what means in English "Nothing". And the storming of Bastille came from the blue sky on this very day.
Such events bring countless tragedies to millions or even billions. And it is all about trying to understand nature of such events, what causes them, and how to avoid, or at least mitgate them.