> Please give me an example of what happens.

It’s easy to forget after 80 years of stable western democracies, but brutal equilibrium shifts do happen. There was a revolution every ~20 years in Europe between 1789 and 1917. And even during the 20th century, the history of much of the world is full of coups, revolts, and uprisings. See all the revolutions in ex-soviet republics, the Arab spring, etc.

So you can pick and choose between the American independence, the French Revolution, the revolutions of 1848, the Commune, and the soviets, to give you just a couple of examples for which you can find some documentation easily.