Ponies wanted Celestia away, because in their minds, she wasn't able to protect them anymore. They forced her to give up the Sun to the Unicorns, taking away most of her powers, and then they threw her out of Canterlot.
Now, a year later, they called her back to Canterlot. Why? What could they possibly want from her?
One shot AU in which the first two seasons happened, but without the presence of the Mane 6 (First attempt at real Pony Fic)...