You cant do the war with one. You need a few.
The Quiet American for the French Involvement
Green Berets, campy propoganda but good for the Advisory Stage
We Were Soldiers for America taking over the war
Full Metal Jacket for Tet
Platoon. Compare the Army of 1965 (We Were Soldiers) to the post Tet Army (even if Platoon was supposed to take place in 67)
When Heaven and Earth changed Places
Hamburger Hill for the last major search and destroy mission
The Killing Fields for the aftermath
There are others....