Its obvious that weapon manufacturers are the one who gains a lot when there is a war since they are the suppliers of ammo and guns used in war. No one really gets benefits in war beside them, a lot of people loses a family member in a war, a country loses a lot of soldiers, and soldiers loses confidence.
War manufacturing is not worth than the lives of the innocent people. They can't just hope for the war so that their deadly weapon industry booms.
Personally, i would say that no one gains from war.
But the question here is who gain's from war? Obviously the weapon manufacturers because they are the one responsible for the weaponry of the military. Nations pay them for weapon supply for sure, without them maybe the weapons used in wars are still both axes and swords or spears. But I agree, people that is affected by this war will not gain anything.