This is the story of SatAM in more detail. Enjoy!
In the year 3234 the planet Mobius is a dark, grim place. Everything is ruled by tyranny, citizens from all across the planet are robotisized everyday, becoming slaves for the tyrant Dr.Robotnik. It is in this time that Sonic and his friends live. He, along with various other recruits, are part of a rebel group known as the Freedom Fighters, led by Sonic and the rightful princess, Sally. They fight everyday to thwart anything Robotnik tries to do to destroy the planet further. Robotnik's reign began when Sonic and Sally were five years old, during a royal ceremony known as "The Coop".
The original king, King Acorn, was sealed away into a crystal dimension known as The Void, and after years of imprisonment turns out to be unable to leave due to his body turning to crystal moments after leaving The Void.
Eventually Sonic and the rest of the Freedom Fighters overcome Robotnik and celebrate, but perhaps it's a little too soon because they forgot to consider Robotnik's nephew and lackey, Snively.