I assume it as self-evident that those who, at any given moment, are the strongest in any civilization, will be those who are at once the ruling class, those who own most property, and those who have most influence on legislation.
The weaker will fare hardly in proportion to their weakness. Such is the order of nature. But, since those are the strongest through whom nature finds it, for the time being, easiest to vent her energy, and as the whole universe is in ceaseless change, it follows that the composition of ruling classes is never constant, but shifts to correspond with the shifting environment. When this movement is so rapid that men cannot adapt themselves to it, we call the phenomenon a revolution, and it is with revolutions that I now have to do.
Nothing is more certain than that the intellectual adaptability of the individual man is very limited. A ruling class is seldom conscious of its own decay, and most of the worst catastrophes of history have been caused by an obstinate resistance to change when resistance was no longer possible. Thus while an incessant alteration in social equilibrium is inevitable, a revolution is a problem in dynamics, on the correct solution of which the fortunes of a declining class depend.