The correct answer to this open question is the following.
To what degree are the modern democratic ideals of voting, open debate, and trial by jury based upon the ideas of the ancient City-states?
These modern democratic ideas indeed are based on the principles of democracy developed by the ancient Greeks, especially the Athenians, one of the most powerful city-states of ancient Greece.
It was Solon in 594 BC, the one who first established some democratic ideas in ancient Greece. However, it was Cleisthenes in 508 BC, who developed the true concept of democracy, allowing Greek men to elect or decide who their rulers would be.
The Greeks influenced the Romans with some ideas about government. The Romans developed the concept of the Roman Law that influenced the foundation of the United States.