Not so intuitive...

1. Go to the /top/territories/forever/ page
   
2. Keep clicking the more button at the bottom
   
3. ... and scroll down until you reach the genesis
   
4. Click and open any territory you might be interested in a new tab to check if the archived tag appears. (those at the bottom are probably archived or new)
   
5. Once you find a territory you want to revive, go ahead to the home menu and hit create at the bottom of the dropdown menu.
   
6. In the name input field, insert the exact same name as the archived territory.
   
7. Then break new grounds and proceed to inherit the old posts.