There seems to be confusion over this achievement.
Visiting a pigeon coop will allow you to acces The Mediterranean Defense Game. Each area is under Templar control. Sending your recruits on missions will gradually weaken the control of the Templars, the weaker they are The easier it is to reclaim the city.
Once you have captured the region you can now perform missions to bolster your level of control, try not to drop below 20%.
You need to capture all 12 regions. Try not to over extend yourself. Otherwise The Templars will regain there presence.
You need to be fully in control of each region for the achievement unlock. If any regions are under siege at the time you Reclaim the last territory then it will not unlock.
If a city is under siege. Press
load the city and a defend the city mission will appear. Send your best assassins and the siege will end.
The territories which appear on the Meditterrean Defense Game have nothing to do with the terrotories you Reclaim from the templars on your main map. The Den Defence game has nothing to do with this.Just ensure you Reclaim all 12 cities and none are under siege.