War happens, but places without a judicial system to solve conflicts between persons, families and regions don't seem to flourish, while many of the more prosperous regions and regions with the most wealth growth feature a judicial system that spans areas normally inhabitated by multiple countries (USA, China, EU, India).

Having a transnational judicial system in the EU (as the most recently formed example) allows coorperation and trade to a much greater extend. Sure, the EU might go to war at some point, but the circle of people and corperations you can trust to respect law and written contracts is very big, no matter if a war is going on or not.