Why were defoliants used in Vietnam?

U.S. military forces used defoliants to remove strategic forest cover and potential food crops used by Vietnamese and Viet Cong forces during the Vietnam War. The primary defoliant used was a chemical mixture named Agent Orange.

Agent Orange was used extensively due to its extremely effective defoliant properties caused by a highly toxic dioxin. It was applied to vegetation by aircraft near any strategic locations, such as military roads, camps and rivers. While useful as a defoliant, exposure to Agent Orange caused serious health effects, such as cancer and birth defects in the Vietnamese people as well as U.S. soldiers.