Since update on 5t July 2012, there is a possibility to conquer guard towers or battle camps. From blog entry:
Conquering towers! You may now conquer remote enemy guard towers on Elevation. By remote I mean towers that can be conquered without interfering with village kingdom. This will reinstate kingdom expansion.
War targets! There are certain war targets such as fortifications and battle camps that can be conquered in order to expand your kingdom as well. These use tower models for the time being.
When you try to conquer a guard tower, you get a 10 minute timer and more tower guards are spawned around you.