Every year on the celebration of Hearth's Warming, ponies put on plays about the founding of Equestria. However, those only show a simplified, foal-friendly version. The actual events were far more dark and violent.
The peace between unicorns, pegasi, and earth ponies only came after the worst war in recorded history, a war which would have led to annihilation if it weren't for the brave actions of a small group of ponies.