The objective of war is to win. In order to do that, we must outsmart our opponent. We can accomplish this by having better weapons (oo, research, building, welding, JOBS!) and better technology (ooo! ditto!) And then when we have the stronger weapons and technology, we can better equip our American troops to go over and fight the enemy. When we send them over, we also send them over with our food...from American companies. Thus employing hundreds, if not thousands more. In turn, helping the American economy.
I still fail to see how it destroys wealth in the American economy.