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.
War will never end as long as the leader's imparted ideology to his followers continues to live.
War kills people and destroy lives. War will never be justifiable when someone has to suffer, specially the innocent ones. Supporting war is like aiding a genocide.