The American Revolution showed the benefit of home field advantage if you are willing to undertake atypical warfare.
In short, the revolution showed that the colonists knew the land that they were on, knew which locals supported them, and knew how to supply and get around the more professional British army.
Rhetros is the right answer
An Irish Catholic settled in Mill Creek Hundred
Harsh jungle environment
difficultly identifying the enemy
demoralization
there was a chemical used called agent orange, but it was used by the U.S. so i dont think it would be categorized as something that american soldiers faced.