truth being that the excessive increase of anything often causes a reaction in the opposite direction; and this is the case not only in the seasons and in vegetable and animal life, but above all in forms of government.

True.

The excess of liberty, whether in States or individuals, seems only to pass into excess of slavery.

Yes, the natural order.

And so tyranny naturally arises out of democracy, and the most aggravated form of tyranny and slavery out of the most extreme form of liberty?

As we might expect.

That, however, was not, as I believe, your question — you rather desired to know what is that disorder which is generated alike in oligarchy and democracy, and is the ruin of both?