I know this has been answered but I’d like to post to see if I understand things myself:
The non-aggression principle says nothing about violence in general being wrong, only the initiation of violence.
If there is no one currently using a certain spot of land, you can build a house, till a garden, take fruit from a tree, build a fence or a wall, without ever having to resort to any sort of violence whatsoever. This is commonly called “mixing your labor with the land.” I really can’t think of any other way for a human being to interact with the earth and ya know- live.
In order for someone else to use these things you have made, THEY absolutely have to resort to aggression (initiation of force,) either by forcing you to not be able to eat a cabbage you grew, or by forcing you to stay out of the building you made. If your friend thinks there is something wrong with defending property ask what would happen if you tried to take her purse. I don’t think there would be anything wrong with her using violence to get it back or having someone else get it back forcefully, and I doubt she would think twice about that either.
Now the second person coming along is claiming ownership (control) but there is a problem, how can the aggressor argue the next stronger force from claiming ownership? In this case the situation turns into might = right and everyone just kills each other in some Darwinian-style contest of survival of the fittest.
Each person would be forced to take as much as possible from the soil as they could until the next warlord came along. The first-user (homesteader) is the proper owner simply because any other option turns into the immediate overuse of land. Humans would just fight it out over over each piece of land, use the land until it is barren, and move on. Not a good way to deal with scarcity- using up Mother Earth’s materials basically all at once.
Luckily, human beings can see beyond immediate gratification unlike most animals. It can be noticed that if I respect another’s land (follow non-aggression principle,) in the long run I can get much more out of the property owner because his vested-interest in his property helps assure he doesn’t overuse the land, and he can eventually gather a buildup of goods (surplus,) as can I on my land. The person who gets good at raising chickens eventually builds a surplus of eggs, and the guy who was just growing corn for his own benefit can also build up a surplus. Now when I have too many eggs or corn I can either let them rot or I can go trade for something else I want.
I’ll direct you to the law of comparative advantage here if you want definite proof that people dividing up work brings more total goods into existence than everyone making all their own crap. More goods = equals more prosperity for EVERYONE! YAY!
Isn’t that what everyone, from the Marxist, all the way to the most capitalist really want, the system that brings the most propsperity for all?
For the long term benefit of individuals and mankind in general the non-aggression principle must be respected. That’s only if you value life and increasing your standard of living though.