The problem for the us military in fighting the vietnam war was b. guerilla warfare was particularly difficult to combat.
The Vietnam War was marked by the extensive use of guerrilla warfare tactics by the North Vietnamese forces and the Viet Cong. The nature of guerrilla warfare, characterized by hit-and-run tactics, use of tunnels and jungle terrain, and blending in with the civilian population, made it challenging for the conventional and technologically superior U.S. military to combat effectively.
The traditional military strategies and tactics used by the U.S. were less effective against the unconventional tactics employed by the North Vietnamese forces.