Communists don't care if thousands of their people die. So to stop them you have to put fear into their soldier's minds. Napalm was their greatest fear. Period. Drop some napalm and the survivors faded away.
After that #2, the AC-47 and later the AC-130. Like napalm, the gunship ended support for battle. It could save a small group in a remote area, far away from artillery support in the night. It was common to put a strobe light in a mortar tube, point it straight up, and somehow the pilot practically put a wing tip over the light and rotated around your position. You were in a cone of protecting fire the VC or NVA wanted no part of. They could put fire so close you felt you could reach out and touch it. In a bar, no AC crew had to buy their own drink if ground personnel were there.