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.
Sometimes war is inevitable and can also lead a huge damage on the country and its people. Some Organization goes to war just to get an economic gains ,territorial gain people who wants to get a hold of the lands , war can be affected by religion too like muslim but not all of them are bad some of them get to war because of their ideals (not all of the muslim is bad).