That's a relatively new idea. It was fundamental to the American and French revolutions, and it was brand new at the time. (The Americans were heavily cribbing off French thinkers, though it took most of a century for the French to implement it.)

It's been the basic claim of liberal democracies for the past 250 years, and they were so successful that people thought it would become universal. But it reached a peak around 30 or 40 years ago -- right about the time that the Soviet Union fell and the "tech age" really got going.

The US in particular saw that as victory for America, and in particular victory for its wealthy class. So it has been leading everything away from liberal democracy.