Defending Alliance Members!!!
I am aware that this is an MMORTS but going along these lines in both types of games MMO and RTS the Alliance members are able to defend each other. I know this is simplified by not being attacked when your offline but as in the AI Castles have enemy reinforcements that come in after a period of time wouldn't it be feasible to allow for alliance members that are online. It would definitely make it more interesting to be in an alliance.
Seek the Word or Embrace the Void!