Ashoka and the Maurya Empire
Ashoka ruled the Maurya Empire, the first to unite most of the Indian subcontinent — and after a war of conquest so bloody it reportedly sickened him, he converted to Buddhism and renounced violence at the height of his power. He had edicts of tolerance, mercy, and moral duty carved on pillars and rocks across his realm, some still standing, and sent missionaries as far as Greece and Sri Lanka. He is history's rare example of a conqueror who chose, at the summit, to rule by persuasion instead of the sword.
A belief system rises, spreads, institutionalizes, and then schisms — changing the rules people accept as legitimate.