How do I retire a Nation?
Click the cog next to a Nation you're an Admin of to reach the Settings page:
On the Settings page, click 'Retire Nation' on the left side:
Click it and you'll see a confirmation screen telling you this action is permanent and it can not be undone.
Also, if you're the only member of a Nation and you leave it, you'll see a confirmation screen telling you the Nation will be closed if you leave and it can not be undone.