Where did democratic ideas and principles originate?

The fastest answer is Athens, Greece around 510 BC. Athens was a powerful Greek city state that was in control of the city and the countryside neighboring the city. The democracy of Athens was a "direct democracy" in that the citizens voted directly on every issue to be considered by the community.

Direct democracy has a number of structural problems but the Athenians didn't have other examples to experiment with. One of the problems, from our modern point of view, is that the qualifications to vote in Athens while attempting to be universal still did not let everyone vote.

Over time successful democracies became "representative democracies" whereby near universal vote (kids can't vote for example) produces representatives such as; Congressmen (MC), Senators, Members of Parliament (MP) who represent the citizens wishes (to one extent or another) in a Congress or Parliament.