War is a necessary evil.
War is a last resort when all diplomacy has failed. To be honest diplomacy can not go on forever. At some point you get and agreement or you don't.
At some point not only rights and principles but also peoples must be protected from aggression and an aggressor.
Diplomacy is a short-lived creature, even when practiced by the best of statesmen.
War is designed as the ultimate extension of diplomacy. As well as the ultimate impeder of aggression. A necessity. A necessary evil.
Don't get me wrong I agree with General Dwight Eisenhower ~ "I hate war as only a soldier who has lived it can, only as one who has seen its brutality, its futility, its stupidity."