Answer:
Borders essentially create guidelines and sets up a countries right to a piece of land. If this is betrayed, it is easy to see who is in the wrong. In messing with the land owned by another country, one might risk the intervention from the United Nations, a sure defeat, or other independent countries aiding in the name of peace or political aspiration. The cooperation as a result stems from the risk of upsetting the peace and having government intervention from others if the resulting wars are lost.