Princess Celestia knew how her kingdom worked. The Unicorns used magic. Pegasi flew in the sky and handled the weather. And Earth ponies... Earth ponies... Huh, maybe Celestia didn't know everything about her ponies. That was about to change.
Celestia and Luna were born as earth pony foals in a dangerous world. They must rise from nothing to become the princess we know, upsetting chiefs, gods, and the very forces of nature in the balance.