The city-state or polis as the ideal form of government

I've been meaning to post something about political philosophy (defined as speculation on what makes for the best government).  Today I would like to promote the city-state.

A city-state, or "polis" from the Greek, but I would like to use a regular English plural (polises) constitutes a central city, close-by other cities and suburbs, and the surrounding countryside.

There are two problems with this form of organization, neither of which would exist if designed right.  The first is that they constantly war with each other (actually not so -- history records the wars and so presents a distorted view of almost continuous warfare, but actually the polis is generally not aggressive.

The other problem is more serious -- empire builders and egoistic Napoleons come along and ruin it.  This is why they are so few.

But look at Singapore and Hong Kong (although sadly in the second case the imperialists are slowly destroying it).

If the whole world were to consist of nothing but such entities, and if they were all set up as functional republics (who almost never go to war with each other -- it is the tyrants of the world where you see invasions and so on), the governments, being far closer to the public, and being such that practically everyone knows the leaders, is just bound to result in better government.

Of course institutions are needed to keep tyrants out of power (legitimate power-sharing checks and balances) and somehow the existing nations need to be broken into smaller units.  That last one is a mouthful -- getting the cities set up as independent and then keeping them so.

I suppose (of course I do it occurs to me) that states like Sparta must be prevented, so some sort of international body chosen by the cities and maintaining basic laws and with resources to enforce them, would therefore be unavoidable.