How, and why, did the ancient greek and latin city-states develop political systems where more than one person ruled?

by Lordford_

I know there was a huge variation in how the political systems in these city-states were structured. The oligarchy in Sparta, the Republic in Rome and the democracy in Athens were very different. I find it fascinating, however, that all of the mentioned, as well as other Mediterranean city-states, were ruled by a collective rather than one person. How did this happen and did it happen other places than in the Mediterranean area?

drylaw

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