The Vietnam War was the conflict between the Democratic Republic of Vietnam(DRV), North Vietnam, and Republic of Vietnam(ROV) South Vietnam. DRV was allied with the Viet Cong, which was a guerrilla fighting force in the South.$^4$ $^5$
The Vietnam war was originally a anti-colonial conflict against the French. Ho Chi Minh, leader of the Viet Minh, the Vietnamese Independence League, and the Vietnamese Communist party, blended anti-French sentiment and nationalism with the Marxist-Leninist revolutionary ideology. in 1954, the Viet Minh was successfully able to to liberate Vietnam.$^5$
In the following peace negotiations in Geneva, Vietnam was split into two. The North, controlled by Ho Chi Minh and the communists, and the South would be non-communist. The USSR and the PRC supported the North, while the US maintained a independent non-communist South.$^5$
In December of 1960 the Viet Cong, formally known as the National Liberation Front, rose to fight the ROV. Following this emergence, a civil war broke out in ROV. During this, the DRV sought to unit both Vietnams under the control of the DRV. In 1961, US expanded its support for the ROV government.$^5$
US involvement in the Vietnam war was fundamentally based on the Domino Theory. This theory states that if a country falls to communism all of its surrounding countries will too. Analogous to dominos falling. To prevent this, US ambassador George Kennan stated that US must do everything in its power to prevent Vietnam from falling to communism.$^5$
In 1964, the DRV had attacked US destroyers in the Gulf of Tonkin. Proceeding this incident, the US approved the use of military forces. The US declared that they will use all necessary measures to repel any armed attack against the armed forces of the United States and to prevent any further agression. The US committed full scale military operations within Vietnam.$^5$
In 1965, Johnson drastically increased the extent of US involvement in the war. He authorized a series of bombing campaigns, including Operation Rolling Thunder. He also committed hundreds of thousands of foot soldiers. Johnson hid the extent of escalation of the war from the American public. He was also a big believer in the Domino Theory and the containment strategy.$^5$
He expanded the war to include Laos and Cambodia. But, at the same time, also promoted the Vietnamization of the war effort. This means that he decreasing ROV relance on US by scaling back the involvement of the US in the war. By 1969, the number of US troops within Vietnam nearly halved.$^5$
The Paris Peace Accords, 1973, laid the terms on the complete withdrawal of US troops from Vietnam. Two years latter in 1975, the DRV achieved their goal of the unification of Vietnam. The country of the Socialist Republic of Vietnam was established. Even though Vietnam became communist, the domino effect did not happen, revealing the flaw in the logic of the theory.$^5$