Kingdoms of the Fallen seems too wordy haha. I really like The Fallen Kingdom, but it seems you've already picked the one you want.
Kingdom of the Fallen is also nice, but if you keep the s on Kingdoms then it just sounds weird to me xD
It would be really cool if you made it so the name plays a part in the server instead of just being a name.
Kingdom of the Fallen could be the main city you start in and as you progress you venture into other Kingdoms or something.