Earth ponies, Pegasi and Unicorns are the three pony races of Equestria
The Pegasi have the special ability to walk on clouds and fly at extreme speeds.
The Unicorns have uncanny magical abilities which are hard to match.
The Earth ponies have only farming abilities and strength.

Earth ponies have no advantage in an unfair life. It's not fair for them. Without any magical properties or wings, they must do everything the slow and painful way. As time has passed on, Pegasi and Unicorns have become more aware of this and have began to tease and insult the poor Earth ponies. With a little push an uprising could begin...