What terrain were the Americans fighting on during the Vietnam war?

The terrain of the Vietnam War changed during the course of the battle. At first, the fields were open and Americans used this opportunity to drop bombs on South Vietnam. However, by the end of the war, the Vietnamese had moved the battlefield into the forests where they knew the terrain well, and Americans could not drop bombs in fear of hurting their own soldiers. This was also a good opportunity for the Vietnamese to set up booby traps in which American Soldiers would find themselves suddenly impaled after setting them off.