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.
Aside from getting another country's resources, another reason to get into war is to well profit from it. War is an expensive endeavor and it needs alot of resources to do so. If you're a multinational arms dealer then if there is war, then people will scramble to get your hardware. If you're weapons are better than your competitors then people will scramble to buy the "bigger stick". Next is, war at times, is a great market manipulator. Alot of money if flowing around and at times, money is frozen still.