Rousseau writes, in Book 3, section 10 of the Contract (The abuse of government and its propensity to degenerate):
There are two general courses by which government degenerates: i.e., when it undergoes contraction, or when the State is dissolved.
Government undergoes contraction when it passes from the many to the few, that is, from democracy to aristocracy, and from aristocracy to royalty. To do so is its natural propensity. If it took the backward course from the few to the many, it could be said that it was relaxed; but this inverse sequence is impossible.
Indeed, governments never change their form except when their energy is exhausted and leaves them too weak to keep what they have. If a government at once extended its sphere and relaxed its stringency, its force would become absolutely nil, and it would persist still less. It is therefore necessary to wind up the spring and tighten the hold as it gives way: or else the State it sustains will come to grief.
He claims that the sequence from the few to the many is impossible. Does the history of modern Europe bear him out?
Without knowing the history of Europe in any great deal, it does appear to me that pre-modern Europe was a patchwork of monarchies & city-states; all are democracies now (with possibly minor exceptions). Does this contradict his assertion?
Or does he mean to say that this inverse sequence, an expansion, cannot be made whilst keeping the integrity of the government? That is without its destruction; for since we're moving from the rule of the few to the many, he seems to be claiming that the nascent democracy, which is to inherit the Government, immediately degenerates into ochlocracy (rule of the mob), and thus destroyed. It will need to reconstitute itself, and is no longer the same. Hence both the pivotal role of the French Revolution & its terror?