Agent Orange

Agent Orange was the most well known and utilised Rainbow Herbicide (a group chemical weapons) during Vietnam. Its purpose was to clear the thick jungles of Vietnam, forcing the Viet Cong to leave their hideouts, and cause peasants to move to urban areas, where the United States had more influence. Agent Orange was sprayed largely due to Operation Ranchhand. It was later found that this chemical contained  2.3.7,8-tetracholorodibenzodioxin, a highly toxic substance, commonly (and for good reason...) abbreviated as TCDD. It is estimated that 12% of the total area of Vietnam had been sprayed with this chemical, causing detrimental effects to both the wildlife and locals. There are infamous pictures of Agent Orange being deployed, that stirred large movements against the substance, and painting an even worse image of Vietnam to those at home int he United States. Unfortunately, as the images are quite graphic, I won't be posting them, but a quick Google search should lead you to them, in case you're interested. The use of this substance was a violation of the 1925 Geneva Protocol, but it was still deployed alongside other chemical weapons until the 1970's, when its use was discontinued. 

Uses of weapons like Rainbow Herbicides and Napalm turned Vietnam into a war that mixed the boundaries between total warfare and limited warfare. It was a clear example of a war that had lost its place, as Vietnam was met with the highest disapproval of any war. It reinforced the notion that a new form of warfare had to replace the new, as times had changed.