How to make money from a nuclear war?

Become a con artist. Distract people, who control the defense money (parliamentarians,  presidents and regular voters) with shiny objects like airplanes or drones that circle around the enemy country ready to hit lifting up nuclear device with missile or laser beam. The shinier the better. What to hide? Hide the fact that the enemy can use cheap diesel-electric submarines to bring the nuclear device to your home country from an unexpected direction. Then close range airplane or drone delivered hits with lasers or missiles are useless. The electric engines make these cheap submarines really difficult to detect.

Alternative shiny object is high precision weaponry that supposedly could be used to destroy all the launching places of the enemy's nuclear devices. What to hide? The high precision equipment is only as good as the information from our spy, some grandpa or other person, that is calling in with the coordinates about the places of our interest. That information is difficult to get from the territory of a smart enemy. Grandpa the spy could be easily jailed, and become useless. Or he can often make mistakes as a grandpa often does. Recent application of precise bombing gave such a poor performance that real civilian deaths exceeded the military's account by shocking 31 times.

Good luck with taking all those billions of dollars. For the rest of us the reality is that as long as nuclear weapons exist the Third World War is impossible since every attacker will be annihilated, precision weapons or no precision weapons, lasers or no lasers.