The "lesson of Vietnam" according to conventional wisdom goes something like this: the US is basically unable to successfully use its military to intervene overseas (and should not even try) because we will invariably pick the wrong side to support in any conflict due to our greedy and immoral national persona, use our military clumsily and ineffectively therefore strengthening our enemies and alienating our friends by the haphazard killing of innocents, and inevitably will be forced to retreat with our collective tails between our legs, leaving the other side victorious and ourselves even more impotent. And besides, violence never solves anything! This is the view of "what happened in Vietnam" that is shared by folks like Senator Kennedy, International ANSWER, and most of those who comprise the liberal base of the Democratic Party.
What really happened in Vietnam? Why did we go, how did we do, and how was it possible that the strongest nation in the history of the world (even at that time) was defeated by a Third World country with no economy to speak of, no industrial base to speak of, and no military to speak of? The long answer would make for a good book (or several). It would include background on the Cold War, US realpolitik strategy, the theory of containment, etc., and an understanding of these topics is important to understanding why the US decided to militarily intervene in Vietnam. However, I only have time and room for the short version.
The US first committed large-scale forces in South Vietnam after the Turner Joy incident, an inconclusive naval gun battle between two US destroyers and some North Vietnamese armed patrol boats. LBJ got the Tonkin Gulf Resolution thru Congress authorizing "all necessary measures" to repel attacks against US forces, and "all steps necessary" for the defense of US allies in Southeast Asia... a veritable "blank check" for presidential direction of military involvement in Vietnam. Shortly thereafter, US ground forces were committed in large numbers.
Originally the US military fought outside the major population areas and generally performed extremely well against NVA and VC forces. The Battle of Ia Drang, popularized in the movie "We Were Soldiers", was the first large-scale fight between US and North Vietnamese forces and although US casualties were heavy (almost 100 killed, more than a hundred wounded) the NVA lost almost 2,000 soldiers during the three-day battle... and who knows how many more due to the B-52 strike on their base camp area immediately following it.
One of the myths of Vietnam was that the US was fighting a largely-indegenous insurgency (the Viet Cong, or "Vietnamese Communists", AKA "VC" or "Charlie" from the radio-alphabetic "Victor Charlie") when in fact the Vietnam War was not an insurgency but instead a very-well propagandized attack by North Vietnam on its neighbor to the south. The US built up its ground forces over the next few years until 500,000 US military personnel were on the ground in Vietnam. Despite tough fighting the US military was successfully eradicating the enemy, at a higher cost in US casualties due to overly-restrictive rules of engagement. The North Vietnamese leadership recognized that it couldn't defeat the US in a stand-up fight and so guerrilla warfare became more prevalent. The use of ambushes, booby-traps (we call 'em IEDs or Improvised Explosive Devices today), hit-and-run tactics, and choosing to fight in populated areas in an attempt to neutralize superior American air and artillery firepower became the favored tactics.
Simultaneously with the US ground war in South Vietnam, the US Air Force and US Navy embarked on Operation Rolling Thunder, a limited strategic campaign designed to gradually escalate against the North Vietnamese until they "blinked" according to a US Air Force memorandum at the time. In that memo, US Air Force Undersecretary Townsend Hoopes, stated:
We believe the enemy can be forced to be 'reasonable', i.e. to compromise or even capitulate, because we assume he wants to avoid pain, death, and material destruction. We assume that if these are inflicted on him with increasing severity, then at some point in the process he will want to stop the suffering.
Therein lies the mistake of Vietnam in a nutshell: assuming that your enemy has the same values, goals, and motivations that you do. In formulating the strategy behind Operation Rolling Thunder, Secretary of Defense Robert McNamara relied on the concept of graduated pressure. Unfortunately for America, McNamara's preoccupation with the idea of treating war as a business situation despite evidence to the contrary doomed our efforts in Vietnam to failure. The North Vietnamese weren't intimidated by pain, death, and material destruction, and only cared about it as it affected their ability to pursue their strategic goal of conquering the South. What the North Vietnamese leadership truly cared about winning, something they had already devoted a decade to, and they were willing to pay any price in order to win if victory was possible.
Operation Rolling Thunder went on in fits and starts, with bombing halts called unilaterally by the Johnson administration as a way of signalling the North Vietnamese "Hey, that hurt didn't it? Come and talk to us now." Instead of productive talking, the North Vietnamese argued over the size of the negotiation table (literally!) and used the relative safety provided by the bombing halts to rearm, rebuild, and re-equip... while targeting restrictions prevented air strikes against North Vietnamese airfields, stockpiled SAMs on levees, and not-yet-complete SAM sites. Hundreds of US pilots were captured or killed due to restrictive rules of engagements, and who knows how many thousands of US casualties occurred in South Vietnam because our air power was arbitarily prevented from being used on logistics in the North by McNamara and his "Whiz Kids".
I can't emphasize strongly enough how the horrors of Vietnam and the tragedies of Southeast Asia that occurred after the war are largely the responsibility of LBJ's moral cowardice and McNamara's egotistical stubbornness that led to the fatally flawed strategy of graduated pressure.
Despite the abject mishandling of our military and the stubborn pursuit of a failing strategy that was criminal in its spending of American lives for no military purpose, the culmination of a couple of years' battle casualties and damage from millions of tons of bombs was having a deleterious effect on North Vietnam's ability to wage war to the point where the leadership became desperate, not unlike the Germans in the Fall of 1944; they were beaten but not defeated. Like the Germans the North Vietnamese decided to husband their resources and launch a devastating series of attacks throughout South Vietnam during the upcoming Tet (Vietnamese New Year) ceasefire. And, like the Germans, they bet all of their military chips on this one shot.
On January 30, 1968, the Tet Offensive started with a series of attacks against US and South Vietnamese forces. Due to poor planning the offensive was poorly coordinated, and the attacks were largely quashed. There were widely-publicized assault by NVA/VC forces including the siege at the US embassy in Saigon, but the NVA and VC forces were defeated and wiped out in almost every case. The North Vietnamese forces were able to conquer the city of Hue and hold it for almost a month, massacring thousands of civilians, until they were defeated and destroyed by the US Marine counterattack, losing 7,500 NVA and VC troops in this one battle. The largest battle of the Tet Offensive was fought at the US Marine base at Khe Sanh, where although US military casualties were in the hundreds, contemporary NVA losses were estimated at 8,000... and post-war information has indicated the NVA lost almost 25,000 soldiers at Khe Sanh.
US Marines in Hue, from Stars & Strips/John Olson via USMC/Combat Helicopter Association
The US and South Vietnam militarily won the Tet Offensive by any objective measure; 3,900 dead (1,000 American) to between 35,000 and 60,000 NVA and VC killed, another 60,000 NVA wounded, 6,000 prisoners taken, and complete control of the battlefield. The initial North Vietnam leadership response to the crushing defeat was to seriously consider a peace negotiation with the US and South Vietnamese. So what changed their minds? The news media and it's flawed reporting of the events.
Sensationalized reporting of the initial attacks by the media fueld the impression that the Tet Offensive was a victory for the North Vietnamese instead of a defeat. Ignoring, and in many cases, denying, the successes of the US and South Vietnamese military, the majority of the press corps reported their perceptions of the battles rather than the facts. The anti-war movement in the US seized upon the reports as proof that the US couldn't win in Vietnam, their rationale being that we couldn't be winning if the North Vietnamese were capable of launching something as widespread as the Tet Offensive. Then, as now, the anti-war movement claimed that the government was lying. More important, the mainstream American public was shocked by the size of the battles and the US casualty figures. LBJ had lied to the American public, not about whether or not we were winning (we were), but about the scope of the war and the extent of US involvement.
The US political fallout from the Tet Offensive ended LBJ's presidential career. With it, support for our presence in Vietnam also ended, and Richard Nixon campaigned and won election on the promise to get the US out of Vietnam. The North Vietnamese were also encouraged that victory was possible, not by militarily defeating the US (which they recognized was impossible) but by killing enough US troops to get the US to withdraw. Accordingly, their strategy changed from taking and holding territory to increasing US casualties regardless of the cost to North Vietnamese forces in order to increase the pressure on Nixon to withdraw. After four years of continued US military success and the drawdown of US troops, Nixon finally got the North Vietnamese to the table by the simple expedient of authorizing unrestricted strategic bombing of Hanoi and Haiphong during Operation Linebacker II in December of 1972. What if this had been done in March 1965?
The North Vietnamese attacked the South in the 1972 Easter Offensive, but underestimated the quality of the outnumbered South Vietnamese forces and their effectiveness when supplied and supported by US air power, resulting in yet another stunning defeat that set the North Vietnamese back for three years. In the interim, Democrats in the US Senate led by none other than our scholar Senator Ted Kennedy managed to gut the legislation that was part of our support for South Vietnam we agreed to at the Paris Peace Accords, and so when the North Vietnamese again invaded in 1975 there was no US airpower to oppose them, no US logistical support to resupply outnumbered South Vietnamese troops facing Soviet- and Chinese-equipped North Vietnamese troops, and no outcry from the United Nations about the violation of international law by the North Vietnamese. After a valiant fight, the ARVN was overwhelmed and defeated, leading to mass imprisonments in re-education camps, hundreds of thousands of executions, and indirectly to the horrific hell of the Cambodian killing fields as totalitarian forces overwhelmed democratic governments in Laos and Cambodia.
This has been a rather long post (more like a Thirty Minute Thought), so let me close with the true lesson of Vietnam and some important corollaries.
The Lesson of Vietnam: Don't fight a war unless you're going to fight to win... but if you do fight, then fight with overwhelming force to destroy your enemy's will to fight as quickly as possible.
First Corollary: A US president must have the moral courage to withstand the fierce personal and political attacks he will receive from his political adversaries, and fight any military action the US is involved in as if 100% of the population is behind him, otherwise he is doomed to military failure and political defeat.
Second Corollary: Wars are won by destroying the enemy's will to resist, so regardless of the disparity in military forces the winner is the one who is left standing on the battlefield.
Read Ted Kennedy's comments again, and also those of President Bush. Then ask yourself which one by his words and deeds demonstrates an understanding the Lesson of Vietnam, and which one is engaging in the same behavior that caused our defeat in Vietnam.