Why were the veitcong so successful against the united states?

The Viet Long were successful against the United States for a number of reasons including:
•They fought on home ground so naturally they knew the terrain better than the foreign American forces
•They used guerrilla fighting tactics which the US were not fully prepared to fight against
•The nature of the terrain was more suited to guerilla warfare than the US's more tactical approach
•Though the US gained ground and won many of the battles, they did not have the man power to secure the land they claimed and thus the Viet Cong prevailed
•Additionally, the Viet Cong had the support of much of Vietnam and had agents throughout towns that were otherwise sided with the American troops