In early history, most societies were governed by a small clique of oligarchs or just one powerful king / ruler. Democracy has been a revolutionary idea that everybody in society should have a say in how they are governed, who governs them, and also gives everybody an opportunity to participate. The evolution of democracy has been a gradual process. Ancient Greece had some of the earliest experiments in participatory democracy, with writers like Aristotle sharing democratic ideas. The principle that everyone counts, enshrined in the practice of giving one person one vote. It's true that the idea was first clearly articulated by Plato. But ancient Athens was nothing like a democracy in our sense of the word: only free men could vote, and only those who had the right parents (and had been in the army). Slaves and women didn't count at all.
In 1215 the King of England was forced to sign the Magna Carta – based on the important principle that the power of a king wasn’t absolute, but subject to approval by (at least some of) his subjects.
Democracy in the modern sense took a long time to emerge: even early English parliaments were elected by a small proportion of the population, and the U.S. constitution (1788) still failed to allow all men to vote, since slavery was only abolished in 1865. New Zealand became the first country to give women the vote in 1893.
It is only in the Twentieth Century that we have seen the widespread adoption of universal democracies with all adults able to vote and take part in the political system.