In his Politics, Aristotle provides the basic principles of political association, and he describes what he believed to have been the process of its development [1]:
Plato was more pessimistic about democracy. He felt that the best hope would be with strong rulers made wise by being trained in philosophy. Aristotle actually put this into practice. He spent three years educating Alexander, the future king of Macedonia at the request of his father Philip.
Greek social philosophy and the political experiments and legislative attempts of their city-states provided the foundations for democratic government, but in practice, these cities ended up being governed by strongmen. The Romans were more successful, although they also ended up with imperial rule. The Roman Republic was the first example of a constitutional government operated on a grand scale and extending over centuries. Cicero, who was a Roman Senator for many years, provided the best articulation of Roman political thought.
The Roman empire was largely ruled by law, and some basic rights were guaranteed to all citizens, but this developed civilization was still capable of sponsoring the savagery of the gladiator games. The final contribution to what is best in Western Civilization came from the East. Compassion and the full sense of an inclusive community are Judeo-Christian contributions.
[1] Aristotle, The Politics, (London: Oxford University Press, 1946).