From Wikipedia

Vietnam: American Holocaust

In the post-war era, Americans struggled to absorb the lessons of the military intervention. As General Maxwell Taylor, one of the principal architects of the war, noted "first, we didn't know ourselves. We thought that we were going into another Korean war, but this was a different country. Secondly, we didn't know our South Vietnamese allies... And we knew less about North Vietnam. Who was Ho Chi Minh? Nobody really knew. So, until we know the enemy and know our allies and know ourselves, we'd better keep out of this kind of dirty business. It's very dangerous."

Some have suggested that "the responsibility for the ultimate failure of this policy [America's withdrawal from Vietnam] lies not with the men who fought, but with those in Congress..." Alternatively, the official history of the United States Army noted that "tactics have often seemed to exist apart from larger issues, strategies, and objectives. Yet in Vietnam the Army experienced tactical success and strategic failure... The... Vietnam War('s)... legacy may be the lesson that unique historical, political, cultural, and social factors always impinge on the military... Success rests not only on military progress but on correctly analyzing the nature of the particular conflict, understanding the enemy's strategy, and assessing the strengths and weaknesses of allies. A new humility and a new sophistication may form the best parts of a complex heritage left to the Army by the long, bitter war in Vietnam." U.S. Secretary of State Henry Kissinger wrote in a secret memo to President Gerald Ford that "in terms of military tactics, we cannot help draw the conclusion that our armed forces are not suited to this kind of war. Even the Special Forces who had been designed for it could not prevail." Even Secretary of Defense Robert McNamara concluded that "the achievement of a military victory by U.S. forces in Vietnam was indeed a dangerous illusion."

Doubts surfaced as to the effectiveness of large-scale, sustained bombing. As Army Chief of Staff Harold K. Johnson noted, "if anything came out of Vietnam, it was that air power couldn't do the job. Even General William Westmoreland admitted that the bombing had been ineffective. As he remarked, "I still doubt that the North Vietnamese would have relented." The inability to bomb Hanoi to the bargaining table also illustrated another U.S. miscalculation. The North's leadership was composed of hardened communists who had been fighting for independence for thirty years. They had successfully defeated the French, and their tenacity as both nationalists and communists was formidable. Ho Chi Min is quoted as saying, “You can kill ten of my men for every one I kill of yours…But even at these odds you will lose and I will win”

The Vietnam War called into question the U.S. Army doctrine. Marine Corps General Victor Krulak heavily criticised Westmoreland's attrition strategy, calling it "wasteful of American lives... with small likelihood of a successful outcome." As well, doubts surfaced about the ability of the military to train foreign forces. The defeat also raised disturbing questions about the quality of the advice that was given to successive presidents by the Pentagon.

Almost 3 million Americans served in Vietnam. Between 1965 and 1975, the United States spent 1 billion on the war (6 billion in FY2008 dollars). This resulted in a large federal budget deficit. The war demonstrated that no power, not even a superpower, has unlimited strength and resources. But perhaps most significantly, the Vietnam War illustrated that political will, as much as material might, is a decisive factor in the outcome of conflicts.

In 1977, United States President Jimmy Carter granted a full, complete and unconditional pardon to all Vietnam-era draft evaders. The Vietnam War POW/MIA issue, concerning the fate of U.S. service personnel listed as missing in action, would persist for many years after the war's conclusion.