system
Given the following post, respond as if you're commenting on Reddit:
human
Can someone explain what the Vietnam War was all about? (ELI5)
gpt
In world history following World War 2, there were two large powers in the world: The United States, and the Soviet Union. Both sides represented competing ideas, and those ideas were capitalism (the idea that customers and stores decide what things are produced and what price, etc) and communism (please see the communism LI5 post). 

The Soviet Union was willing to help other countries out financially (with money) provided they would think about converting to communism. Since most communist nations at the time were run by one guy in power, this appealed to several people who wanted to run their own country like kings used to. 

 France happened to have some colonies in Asia that they watched over and made money off of without really helping the people that much. After World War 2 ended, the world kind of started to bug countries like France and the United Kingdom to let their colonies be free. This was not something that was well accepted by those countries and they held onto colonies were they could. 

 Meanwhile, people in Vietnam (called French IndoChina at the time) wanted to be free and started looking for people to help them. The Soviet Union's powerful stance as a communist nation had helped encourage other nations to do likewise, and so the People's Republic of China was created and became communist as well. Since China was so close, this made them a logical choice for Vietnam to seek help from.

 The United States, had decided that it did not like communism and it did not like countries like the Soviet Union and the People's Republic of China spreading their ideas around the world. Once it became clear that communism was a possibility in Vietnam, the United States decided that it would step in and prevent this from happening.

 The trouble with fighting in Vietnam was that there were no clear battle lines, and the "bad guys" could be anywhere. Also, troops were rotated in and out of Vietnam on a regular basis, so they lacked experience with the area and were more likely to "freak out" and commit horrible, horrible actions.

 Opposition rose at home in the United States, partially because it was seen that the North Vietnamese just wanted their freedom from colonial rule, much like the U.S. once did... and partially because the man that the U.S. had decided to support was corrupt and not very smart. When the United States decided that maybe he wasn't the best man to lead the South, they let his generals know that they would support the people that took over. They killed the leader and took over, though none of them were as good as the guy that they'd killed, which isn't saying much for anyone. 

 As the U.S. switched Presidents after the assassination of John F. Kennedy, the new president (Lyndon B. Johnson) decided that the country could win the war... but since this was not a war of seizing ground (since the Vietnamese would run away when attacked) it would have to be a war of attrition... which is to say, whoever kills the most people wins. The U.S. conducted search and destroy missions and kept a body count to prove that they were winning. But eventually, public tide turned fully against the war and the United States saw that it would be foolish to continue to supply the assets needed to fight, so they left. 

 Within a year of their leaving, the North Vietnamese conquered the South, executed the leader there, and united the country as Vietnam.

 By the end of the 1980's the U.S. had reopened diplomatic ties with the nation and it now enjoys favored trade status with the country.

 (Simplified, left out names of organizations and leaders to just get the general idea of what happened and an overview of the war)

 Concise edition: the Vietnam War was about the U.S. halting the ideas of countries like the Soviet Union and the People's Republic of China. It was conducted because the U.S. felt that their isolationism had helped bring about WW2 and Europe's policy of appeasement... so... the U.S. would stick it's nose in everyone's business and smack down those who tried to rise to power... dictators... Hitler-esque peoples... etc.