Vietnam was an undeniable failure for the United States government. Despite expending more than $141 billion, and 56,000 American lives, the world’s largest military superpower was unable to achieve its sole strategic objective: to prevent Vietnam from falling under communist control. Historians are deeply divided over the reasons that led to US defeat. Most attribute the loss to several factors that each played a role. This topic offers an overview of those factors, with careful consideration of the evidence that both supports and refutes each claim as a viable reason for defeat.