What's the point of war in the modern world? Gain land/people? If there's a thriving economy there, war will probably change that quickly. If there's no thriving economy, what's the point? You could try to exploit the people/resources there, but the profits in that seem (at least compared to a world power) pretty thin. Unskilled labor and unimproved land are just not worth what they used to be. Specific resources mig…
The point of war in the modern world may in fact be the denial of a thriving economy or industrial base to an adversary. For instance in a large scale nuclear war many of the plans call for the destruction of enemy nuclear weapons as to protect your own infrastructure/population and to destroy enemy infrastructure/population to gain an economic and industrial advantage after the war ends.
War is also not always an economic calculation: humanitarian concerns, revenge, fear, upholding the law, alliances and thoughts of glory can often motivate a conquest that holds no real value to the victor.
Why did Alexander engage in his wars? He didn't seem to particularly enjoy the job of government.
What was the economic value to Rome of destroying Carthage?