Ownership is a conceptual association of some actor (individual, institution, etc) with a resource. An owner will have some special privileges with respect to the resource. Ownership may mean exclusive access but it may entail other special privileges.
Contrast this with possession. Possession is a physical description of reality.
Possession is necessarily coupled with violence. Ownership may be coupled with violence like with statism, or it may not be coupled with violence like with folkism.
If an actor possesses a resource without the consent of the owner this is unjust. I consider the previous statement to be a tautology.
You can consider 3 levels of ownership.
This site is not concerned with the formal level. That is just rules issued by a sovereign. I will focus on the informal and the sovereign.
I wish to draw your attention to how most people treat these differently. On the informal level people are quite peaceful, escalating to destruction only when their ownership associations are not respected. Violence is used (at most) as a corrective function to bring reality closer to their ideal. On the sovereign level they will reward violence with ownership. For example, the French people treated France like it belonged to the French government. After all, the French government was the last one to successfully fight for it. Then the Nazi war machine successfully fought for the territory and the French people treated the Nazi's as the owners of France. People consider the owner of land to be the last group to successfully conquer it. On the sovereign level people reward violence with ownership. This is currently untrue for a small minority of radical individuals.
This site suggests a unification of methods between the informal and the sovereign levels.
Meta Politics