Can you explain what's the reason? You can say positive as well as negative reasons.
I think the most common reason for war is the urge to capture resources owned by another jurisdiction. For example, the USA frequently goes to war to secure access to energy resources.
First, the causes of war are caused by reasons of economic gain, measured in terms of the acquisition of natural resources such as gold, silver, oil, or trade monopoly or market access, raw materials and investments5. This was stated by Hedley Bull in his book Hedley The Anarchical Society A Study of Order in World Politics.