The year 1968 brought several significant milestones to the Vietnam War, such as a major offensive, the breakdown of peace talks and the decisive turning of public opinion against the war. After 1968, the mainstream opinion in the United States was that the war had been irretrievably lost.
1968 opened in Vietnam with the siege of the Army firebase at Khe Sahn. Though this action was relatively small in scale, it later became part of the massive Tet Offensive in which hundreds of thousands of Viet Cong and North Vietnamese regulars struck U.S. positions all over the South. Despite the successful American counter-offensive, the size of the offensive convinced many Americans that the war was not winnable by conventional means.
On March 16, 1968, elements of the 23rd U.S. Infantry Division sacked the village of My Lai, killing over 500 civilians. The event, exposed a year later, helped drive public opposition to the war and resulted in minor disciplinary action against some Army officers.
In October, peace talks in Paris broke down when the government of South Vietnam withdrew from the process. The collapse of talks damaged the presidential campaign of Vice President Hubert Humphrey, who narrowly lost the November election as a result.