Why could the US not win a quick victory over the vietcong and what was the effect?

The reason why the United States could not win a quick victory over the vietcong was: because they engaged in guerrilla tactics of quick attacks and disappearing into the jungle.

Because we're fighting on their homeland, they simply know the terrain bettwe than we did. The result was a loss of morale among US soldiers due to constantly have to experience massive loss.