system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The Vietnam War

I've just started studying this at school and I'd like it explained to me simply before I start analysing all the reasons it failed. I'm not American, I'm only 14 and so my only real exposure to this war is Forrest Gump, Full Metal Jacket, knowing it was about stopping the spread of communism and two history lessons.
gpt
Vietnam was a country controlled by France for many years. There were popular movements against the French, and during ww2 nam was controlled by the vichy French(nazi puppet govt of France). Ho chi min led a movement and declared independence for Vietnam(using words reminiscent of USA declaration of independence) . Allies won ww2, Vichy sorta leaves, regular French govt comes back, puts down "dissidents", but is not having easy time. Appeals to Usa for $$$. USA provides a few heli's and gorilla training to local Vietnamese. France sees no victory, pulls out. USA sends in troops to "stop spread of communism", or, in some historian's opinions; to distract from attention from the civil rights and union rights movements that were growing at the time. 

They'll probably try to tell you about the gulf of tonkin incident in school. Read "a peoples history of Vietnam" so you can be prepared to debunk teacher if he starts feed you bullshit.