Agent Orange was used in Vietnam for a couple of reasons. Agent Orange a chemical defoliants, which means it kills live plants.
This war was fought in really thick jungle areas and the North Vietnamese were used of this kind of terrain and they used it to their advantage. Many U.S. soldiers lost their lives because they were in unfamiliar territory and were ambushed by Vietnamese soldiers hiding in the jungle. So, 'Agent Orange' was used to eliminate forest cover for North Vietnamese soldiers.
Another reason they sprayed 'Agent Orange' was to kill the crops that might be used to feed the Vietnamese soldiers.
Hope this helps. :)
