actually, the magic figure for an organized dispute resolution system (what courts,
lawyers, and judges are) is about 50,000 people. up to that point, you can
have decentralized (or even informal) dispute resolution systems work.
once you have that many people, you have to develop a centralized dispute
resolution system or you won't be able to resolve the issue of stability for the
continued growth of the society (and stability comes from (a) lack of personal
vendettas to resolve problems; and (b) a coherent code by which all citizens
can live and expect others to live)
at least according to Jared Diamond, author of Guns, Germs, and Steel