Why is war the way to settle a dispute?

Though war is almost universally frowned upon by most civilized nations, this doesn't change the fact that many of these nations have been—or are currently involved in—some sort of violent conflict.
There are many who oppose war without reservation; however, others feel that war is a means to an end when negotiations and other peace-keeping efforts fail. Most free countries look at war as a means of preserving their own freedoms and ways of life. Once a country feels that its rights are infringed upon, the country becomes more likely to engage in a violent conflict to protect its interests.
Some have argued that war ends up preserving more lives than it costs. It has been argued that war allows for the separation of societies and people who otherwise would not get along. Instead of forcing these people to live together, war allows for like-minded people to live in separate societies. 
Others argue that war allows for nations to better control their own financial interests. This ultimately leads to more prosperity and supposedly more happiness in the countries who are victorious at keeping outside influences out of their countries.
https://fee.org/articles/why-war/