I could go for this being a 'guild' feature - however, it would require that an entire guild be within the location together. At that point (assuming it's a sizeable guild) who is going to oppose them?
Also, i'd be game for a capturable castle type arrangement. However, this would require you to keep a sizeable army in that castle for defense.. and prevent you from using your forces for other activities. You'd have to defend your stronghold and that castle.. between that, you probably wouldn't be able to attack or really do anything else. However, it would give people something solid to attack, etc.
"He uttered the word of curse, crush him with our Orcish iron!"