Who Won the Vietnam War?
It is not as simple as saying that one side or another won The Vietnam War because to do so indicates that one does not understand that nature of the conflict and the complexities of the situation.
A Complex Question
The first response to the question: "Who won the Vietnam War?" should always be: "Which war are you talking about?"
A person only familiar with the role the United States played in Vietnam might ask this question expecting one of two answers: "The United States won" or "Vietnam won". Unfortunately, the phrase "The Vietnam War" covers a much longer period of time in the country of Vietnam where the phrase probably has very little meaning. For the Vietnamese, the closest description of the phrase "The Vietnam War" involved a conflict that spanned almost a hundred years during which the Vietnamese attempted to expel foreigners from their country and rule the country themselves.
From approximately 1887 to 1974, Vietnam was "occupied" by foreigners including the French, Chinese, Japanese, and Americans where the Vietnamese did not have control of their own government. Although the Vietnamese were not fighting what Americans would normally classify as a war, there were strong insurgency movements within Vietnam fighting to expel the foreigners from their country. The most notorious battle prior to American involvement occurred at Dien Bien Phu and on May 7, 1954, Vietnamese forces defeated the French and expelled them from the country.
Following the defeat, the Geneva Accords split the country at the 17th parallel. China exerted influence on the North through the government in Hanoi while the U.S. started to build a presence in the South by sending advisers. The intent of the U.S. government was to establish an independent government in South Vietnam and that was always the definition of victory for the U.S. Unfortunately, it never happened, which is the primary thing that muddies the waters when somebody asks who won the Vietnam War.
In coming to a conclusion about an answer to the question of who won, I won't use too many more factoids to explain. American involvement effectively began after the French defeat with the intent to create a stable government. The reason for this involved adherence to the "domino theory"; the belief that if something wasn't done in a country that bordered a Communist country, it would fall to Communism. This was the main theoretical underpinning of U.S. involvement in Vietnam.
For a variety of reasons, advisers turned out not to be enough, and starting in the early 1960s, American troops started to filter their way into the country, eventually leading to full-scale involvement in 1965. When Marines were sent into Vietnam in March of 1965, it was considered the beginning of the ground war.
When somebody asks about winning or losing Vietnam, they are usually thinking in terms of fighting and casualties and here is where defining "loss" in Vietnam becomes difficult. In terms of fighting effectiveness and casualties, the U.S. did not lose the war in Vietnam. U.S. troops suffered just over 48,000 deaths in Vietnam compared to estimates that range into the millions for the Vietnamese. U.S. troops rarely lost a battle, though the entire concept of what constituted a "battle" was turned completely upside-down in Vietnam. Guerrilla warfare does not have battles in the conventional sense. To say the U.S. lost the Vietnam War (which was never officially declared a "war" incidentally), is to cover the troops under an umbrella they do not deserve and is why when we say the U.S. lost, it requires explanation.
The logical question that rises from the last paragraph is this: "If the United States military killed more Vietnamese and was not technically defeated, how did the U.S. lose the war?" Again, we come to the answer involving complexity. Ultimately, the U.S. lost the war. They didn't achieve their goals. There were two main reasons for this. One was political and the other was what I'll call logistical. In my favorite book on the Vietnam War, Loren Baritz's "Backfire", the author provides the logistical reason why the U.S. couldn't win in Vietnam. Essentially, he argues that the U.S. military was designed, at that time, to fight wars like those in World War II and Korea. Effectively, wars where two forces clash and the better trained, more powerful force usually wins. In Vietnam, the U.S. military simply couldn't adapt to the requirements of guerrilla warfare (and that doesn't mean the soldiers couldn't adapt, they could. It means the military organization couldn't adapt.). The very nature of the U.S. military made it impossible. This answer requires a much more in depth explanation and that is covered in Baritz's book.
The other answer, the political answer, is that popular opinion in the U.S. turned against the war (with good reason), making further commitments of troops and money impossible after 1968. At the time, a lingering war where no perceivable progress was being made for a goal that most Americans couldn't understand made supporting Vietnam political suicide. No administration, no politician, could continue to support the conflict in Vietnam and expect to get re-elected.
The U.S. defined "winning" the "war" as the establishment of a stable, independent government in the south. This goal was never achieved and is why the effort in Vietnam by the U.S. is considered a failure.
Another common question asked and answered on radio talk shows and the like is: "Could we have won the war in Vietnam?" Many who do not understand the complexities of the conflict often answer the question with an emphatic "yes!" Such a statement represents a colossal misunderstanding of the conflict. That "yes" most often means that the U.S. could have won the war militarily by bombing more or dropping a nuclear weapon. This was impossible.
The problem with "winning" in Vietnam had to do with a basic misunderstanding the U.S. had for the causes of Vietnamese opposition to the American presence there which had less to do with Communism and any influence from China or the Soviet Union and much more to do with Vietnamese nationalism. This nationalism spread throughout the entire country and was why the U.S. was fighting insurgents in both the North and the South. To "win" the war by extended bombings or nuclear weapons would have meant destroying South Vietnam as well as North Vietnam.
Due to Vietnamese nationalism, many people, myself included, believe that the U.S. could never have won the "war". As evidenced by the massive Vietnamese casualties, the people of that country were determined to drive out any invading forces and were willing to fight to the death to do it. As evidenced by the political opposition within the United States that helped turn American public opinion against the war by 1968, the American people were unwilling to accept more casualties to fight a conflict with no end in sight.
The U.S. certainly did not win the war, but the military did not exactly lose it either. It was a conflict that the U.S. did not have any chance of winning because the politicians who determined the goals of the war never understood what motivated the Vietnamese. Just remember that the Vietnam War can be a very sticky, sensitive subject and defining the U.S. role as a "win" or "loss" is too simplistic an explanation that characterizes the roles of many different people, from politicians to military grunts, without proper context.