Unless you are reading something that gives a specific list of the “horrors of Vietnam,” this phrase can simply be used to refer to the various terrible things that went on in this war and the ways in which the war was horrible for the people who experienced it. All wars are horrible, and Vietnam was no different. It was horrible for those who were fighting and for those who were caught in the middle of it. Let us look at some things that could be called “horrors” of this war.
For average Vietnamese who were trying to stay out of the war, there were horrors. For example, the Vietcong might kill them if they did anything that was perceived as helping the Americans or the South Vietnamese government. On the other hand, Americans might destroy their homes if they were seen to be helping the Vietcong. Average Vietnamese had to deal with the devastation caused by bombing and by the spraying of herbicides over the countryside. These were clearly “horrors.”
For those fighting, there were “horrors” as well. For the Americans, there was the horror of having to worry about an enemy that could strike anywhere. This was not a “regular” war where the enemy all wore uniforms. Instead, any person could be a guerrilla. Worrying about this, along with things like mistakenly killing people out of fear that they were guerrillas, was a “horror.” For the Vietcong and the North Vietnamese, there was the “horror” of napalm attacks. These things were in addition to the more general horror that goes along with any combat.
All of these things can be seen as examples of the “horrors of Vietnam.”