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.
If your country is involved with it or if someone is attempting to take over your resources or your country's freedom you will surely not hesitate to fight for it. We all know that being in a war only waste lives and resources, but if involves your freedom, it will be worth the risk.