if you're asking what hindered the US from winning in Vietnam it was cause of multiple factors
first one and probably the biggest is that the war was unpopular back in the US most of the population found it to be a pointless war
second reason would be that the Soviets and us Chinese were training equipping and supporting the Viet Kong
third reason would be that the Viet Kong were excellent guerrilla fighters and knew the land better than the American GIs
