To avoid spoilers, check out everything after the break!
This is going to be epic for all the pony history people out there. I guess Equestria actually did have some conflict between the different races.
And the new synopsis:
In “Hearth’s Warming Eve” the six friends are honored to put on Canterlot's most important play of the season, the Hearth's Warming Eve's holiday pageant that illustrates how Unicorns, Pegasi and Earth Ponies put aside their differences and founded Equestria.Maybe we will get a bit more information on Earth ponies?