1000 years ago, Princess Luna realized how many pony love Her night. Years after years the ponies devided into two groups. Whose living in daytime, and whose living in nighttime. The first group's ponies firstly accepted the night ponies, but this happy times slowly gone and the day ponies started hating the night ponies.
And this hate not just in Equestria, every creature whose love nights get worse slanders.
Ponies, Batponies, Changelings, Griffons and Hippogriffs groups come to Luna ask for help, but when Luna try to talk about that with Celestia, she do nothing. Luna anger is growing and growing. Once when she got enough Luna choose the best option and she lead her new people into a new place, where they can live in peace.