Major motive of U.S was to destroy the greenery of Vietnam as the Vietnamese used the forests and trees to hide. So the weapon used for destroying the forest was Agent orange which destroyed the forests and the crops.
The other weapon used was Napalm which was a very dangerous bomb which was considered very inhuman because it was a bomb which burnt the part of the body where it fell. This lead to many deaths of the Vietnamese and the U.S also had the best plane named P-90 which could bomb many missiles at a time.