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.
There should be no reason to support war. Where innocent lives are at stake. War should not be supported at all means. If it is to protect lives and self defense, then it's tolerable but if it is just to prove the power of a certain group then much better to stop.