Consider that even today, in this statist world, there are agreements to the “rules of war”. States agree that certain people are off-limits, such as civilians or medics. Now, states violate these rules all the time, but states also don’t believe that aggression is immoral, so what else would you expect?
So, would a libertarian nation target civilians? Of course not. But your question was targetted at “the enemy”, which I can only assume to mean the members of the invading army. Well, I doubt that a libertarian army would target medics. Why? Well, it is clear that medics are non-aggressive. Of course, it is always possible that an individual in the libertarian army might target medics, but he would be breaking the NAP, so there is no reason to assume this course of action would be widespread, and there is nothing preventing the family of the victims from pressing charges after the war is over.
Of course, that is probably an unlikely outcome, but what can I say? The NAP is a legal code, not a moral code. The NAP is just a legal version of the golden rule. Not every person in a libertarian nation is going to be a stand up citizen. But, considering it would be a nation based upon the NAP, those sorts of war crimes would be very limited, and they are not even necessary to defeating the invading force.
And the more I think about it, it’s not entirely clear that the medics are not aggressive. Consider 2 people break into your home. One of them fights you, but the other does not. The one that doesn’t fight makes sure that the other one can continue to fight. Is the second person fair game for you to fight? Of course! He has invaded your house, and he is actively making sure that his partner in crime can continue to aggress against your person.
So, it might be the case that even medics are fair game in an invading army. I haven’t thought about it a lot, but it seems that they are aggressing.
I covered some of this in the above portion, but the important thing to keep in mind is that the invading army is by definition violating the NAP. So, there probably aren’t that many rules necessary for defending against an invading army. More or less:
-
Repel the invaders
-
Don’t aggress against civilians
EDIT: I didn’t write anything about the rules of war for an invading force, so here it is:
An invading army cannot invade without violating the NAP. Any rules of war based on the NAP are obviously going to do nothing for them. But what about a small strike force? Well, theoretically, if the force is small enough, it could get around a city or nation without using aggression in order to accomplish its mission. So, the rules:
- Don’t aggress against anyone, civilians or otherwise.
I guess that’s it. If the libertarian nation is sending a force into a state, well, then there really isn’t any need to follow the NAP, as the state doesn’t follow the NAP anyway. Just being there violates the laws of the state. And who is going to bring charges against them in their home nation? If the force goes to another libertarian nation, then so long as they don’t break the NAP, it is unlikely to be a problem.
There are two things to keep in mind. The first is that drastically “underpowered” armies have been able to successfully repel “overpowered” invaders. The second is that defending armies can lose, even today in the statist world. Consider Nazi Germany. It had a very powerful army. But it did lose.
There are no certainties.