I guess the question is Why? Why would anyone sign up, and why would the kingdom's intentionally create such a barrier between their kingdoms? A self-administered peacekeeping force?
Without bringing into effect modern ethics 'Save the Trees' why would the kingdoms spend resources providing recruits - who could be useful soldiers, armies, etc? Why would they want an uncontrolled military force on their borders? Go to Comment
Small tavern in an out of the way town. Serve a wonderful delicacy that is simply outstanding. It is a creamy white consistancy, sweet, good to eat alone or a sweetener on any dessert.
If the explore or ask they are shown where they get it. They breed a group of large catipillars or some other type of insect that basically spit the product onto a setup that they created for that particular reason. Or maybe the delicacy is the byproduct of feeding them something.