This film spoke for a generation of betrayed Vietnam Veterans conveniently forgotten by not only their government, but by the very American people they thought they served. The controversial geo-politics of the Vietnam war prevented a total war military victory from being rapidly achieved by weasels like Robert Mcnamara and four star clowns like General Westmoreland. Instead they tried the calculated low intensity conflict approach that all but guaranteed prolonged military failure and escalation against the motivated, and battle hardened Viet Minh/Viet Cong cadres in the South/NVA regulars in the North.
An example: The US Joint Chiefs of staff requested the mining of Haiphong harbor in 1964, it was not finally undertaken until Operation Pocket Money in May 1972. 85% of North Vietnam's war material, weapons, ammo, SAMS, and fuel came through Haiphong.
Rambo's monologue states truth: "And I did what I had to do to win! But somebody wouldn't let us win!"