The document discusses why US forces failed to defeat the Vietcong in Vietnam. The Vietcong were effective because they used guerrilla tactics like ambushes and hit-and-run attacks. This frustrated the US army and led to more support for the Vietcong from South Vietnamese peasants. Despite superior technology and resources, the US struggled against the Vietcong's guerrilla tactics, intimate knowledge of the local terrain, and tunnels. The document examines sources that illustrate the Vietcong's strengths in guerrilla warfare and popularity with civilians, as well as their weaknesses in resources compared to the US.