Instructions
Speak with the leader of your alliance about your decision to leave.
Return any special items or currency granted to you by the alliance. Returning these materials ensures the alliance doesn't suffer too great a loss with your departure; everything you take with you must be replaced by other alliance members.
Use the in-game alliance chat channel to announce your decision to leave at least a week before you go. This gives the alliance time to build a defense strategy to fill the hole your territory leaves in their sovereignty.
Work with alliance members to promote a new officer to take your place if you serve in a leadership role.
Leave politely and thank alliance members for their help. If you leave on a good note, you may be able to re-join later, and alliance members may still support you in an emergency.