There are many factors that can be cited as cause of the My Lai Massacre. Among them are:
- The general nature of the war in Vietnam. Much of the war involved American troops fighting irregular guerrillas who were not in uniform. This made it extremely difficult to distinguish between enemy fighters and civilians.
- Orders on the part of various members of the command structure. The soldiers who went into My Lai were told in briefings that no one other than Viet Cong members would be in My Lai at the time that the soldiers went in. There are also conflicting accounts regarding what was said about who could legimitately be killed in this raid.
- Stress experienced by the soldiers. War is inherently stressful and can cause people to do things that they would never have done in more normal circumstances.