Perhaps this theory of the natural transformations into each other of the different forms of government is more elaborately set forth by Plato and certain other philosophers; but as the arguments are subtle and are stated at great length, they are beyond the reach of all but a few.
I therefore will attempt to give a short summary of the theory, as far as I consider it to apply to the actual history of facts and to appeal to the common intelligence of mankind.
For if there appear to be certain omissions in my general exposition of it, the detailed discussion which follows will afford the reader ample compensation for any difficulties now left unsolved.
What then are the beginnings I speak of and what is the first origin of political societies?
When owing to floods, famines, failure of crops or other such causes there occurs such a destruction of the human race as tradition tells us has more than once happened, and as we must believe will often happen again,
all arts and crafts perishing at the same time, then in the course of time, when springing from the survivors as from seeds men have again increased in numbers
and just like other animals form herds — it being a matter of course that they too should herd together with those of their kind owing to their natural weakness — it is a necessary consequence that the man who excels in bodily strength and in courage will lead and rule over the rest.
We observe and should regard as a most genuine work of nature this very phenomenon in the case of the other animals which act purely by instinct and among whom the strongest are always indisputably the masters —
I speak of bulls, boars, cocks, and the like.It is probable then that at the beginning men lived thus, herding together like animals and following the lead of the strongest and bravest, the ruler's strength being here the sole limit to his power and the name we should give his rule being monarchy.
But when in time feelings of sociability and companionship begin to grow in such gatherings of men, than kingship has struck root; and the notions of goodness, justice, and their opposites begin to arise in men.
Walbank Commentary