To understand Ken Burns’ 18-hour Vietnam documentary, listen to the music. The haunting score tells you: This will be a tale of misery. And indeed, Burns and his co-author Geoffrey C. Ward conclude their script by writing, “The Vietnam War was a tragedy, immeasurable and irredeemable. But meaning can be found in the individual stories . . .”

The film is meticulous in the veracity of the hundreds of factoids that were selected. Everything depicted on the American side actually happened. But that the chosen facts are accurate doesn’t mean the film gets everything right. Indeed, the brave American veterans are portrayed with a keen sense of regret and embarrassment about the war, a distortion that must not go unanswered. And the film implies an unearned moral equivalence between antiwar protesters and those who fought.

Burns’ theme is clear: A resolute North Vietnam was predestined to defeat a delusional America that heedlessly sacrificed its soldiers. The film follows a chronological progression, beginning in the ’40s. Right from the start, harrowing combat footage from the ’60s is inserted to remind the audience that a blinkered America is doomed to repeat the mistakes of the French colonialists. The main focus of the documentary is the period of fierce fighting from late 1965 to 1972.

Against a gripping assortment of close-up photos and combat video, dozens of American and Vietnamese voices offer snippets of personal insights about history, geopolitics, families, ideologies, politics, battles, casualties and, above all, frustrations.

Most of the interviewees talk in the lugubrious tones of the defeated. We all know the story ends badly. But when it’s over, we aren’t told why we lost. The music is more memorable than the pictures, and the pictures are more compelling than the narration. We are deluged by sights and sounds but not enlightened as to cause and effect.

An American lieutenant who fought there in 1965 is quoted at the end of the film saying, “We have learned a lesson . . . that we just can’t impose our will on others.” While that summarizes the documentary, the opposite is true. Wars are fought to impose your will upon the enemy. If you don’t intend to win, don’t fight.

Our civilian and military leaders were grossly irresponsible. At the height of the war in 1968, Secretary of Defense Clark Clifford is quoted as telling President Lyndon Johnson, “We’re not out to win the war. We’re out to win the peace.”

Our senior leadership granted the enemy ground sanctuaries in Cambodia, Laos and North Vietnam and bombing was severely restricted.

The North Vietnamese were superb light infantry. The film points out that we grunts called the DMZ (Demilitarized Zone) the Dead Marine Zone because we were pounded from North Vietnam and forbidden to attack. The real lesson: Never fight on the enemy’s terms.

The documentary includes a modicum of footage about the South Vietnamese military. The South Vietnamese soldiers I fought alongside were brave and determined. Yet in 1973, sick of the war, Congress forbade any further bombing in Southeast Asia. Military aid to South Vietnam was slashed, while Soviet-built tanks and Chinese-made artillery poured into North Vietnam.

It is moot whether South Vietnam could have survived had our aid continued. The video of our panicked final pull-out in 1975 is flat-out depressing.

The film casts the antiwar movement in a moderately favorable light. Air Force pilot Merrill McPeak is quoted as saying, “the antiwar movement itself, the whole movement towards racial equality, the environment, the role of women . . . produced the America we have today, and we are better for it.”

Are the protesters the real heroes here? What about the valiant US soldiers, 75 percent of whom were volunteers?

This documentary succeeds in vividly evoking sadness and frustration. But that is not all there was to the story. “The Vietnam War” strives for a moral equivalence where there is none. The veterans seem sad and detached for their experience, yet 90 percent of Vietnam War veterans are proud to have served. So there’s a large gap between what we see and the attitude of the vast majority of veterans.

Their sense of pride — so vital for national unity — is absent from the documentary. And that’s a glaring omission.

Bing West served in Marine infantry in Vietnam. He is the author of “The Village,” which has been on the Marine Commandant’s reading list for 45 years.