The September 1964 South Vietnamese coup attempt took place before dawn on September 13, 1964, when the ruling military junta of South Vietnam, led by General Nguyn Khnh, was threatened by a coup attempt headed by Generals Lm Vn Pht and Dng Vn c, who sent dissident units into the capital Saigon. They captured various key points and announced over national radio the overthrow of the incumbent regime. With the help of the Americans, Khnh was able to rally support and the coup collapsed the next morning without any casualties.

In the immediate month leading up the coup, Khnh's leadership had become increasingly troubled. He had tried to augment his powers by declaring a state of emergency, but this only provoked large-scale protests and riots calling for an end to military rule, with Buddhist activists at the forefront. Fearful of losing power, Khnh began making concessions to the protesters and promised democracy in the near future. He also removed several military officials closely linked to the discriminatory Catholic rule of the slain former President Ng nh Dim; this response to Buddhist pressure dismayed several Catholic officers, who made a few abortive moves to remove him from power.

In part because of pressure from Buddhist protests, Khnh removed the Catholics Pht and c from the posts of Interior Minister and IV Corps commander, respectively. They responded with a coup supported by the Catholic-aligned i Vit Quc dn ng, as well as General Trn Thin Khim, a Catholic who had helped Khnh to power. Having captured the radio station, Pht then made a broadcast promising to revive Dim's policies. Khnh managed to evade capture and, during the first stage of the coup, there was little activity as most senior officers failed to support either side. Throughout the day, Khnh gradually rallied more allies and the U.S. remained supportive of his rule and pressured the rebels to give up. With the backing of Air Marshal Nguyn Cao K, commander of the Republic of Vietnam Air Force, and General Nguyn Chnh Thi, Khnh was able to force Pht and c to capitulate the next morning, September 14. c, K and Thi then appeared at a media conference where they denied that any coup had taken place and put on a choreographed display of unity, claiming that nobody would be prosecuted over the events.

Convinced that Khim was involved in the plot, Khnh had him exiled to Washington as ambassador, and eased General Dng Vn Minh out of the political scene, thereby removing the other two nominal members of the ruling triumvirate. However, concerned that K and Thi had become too powerful, Khnh had Pht and c acquitted at their military trial in an attempt to use them as political counterweights. Despite his survival, the coup was seen by the historian George McTurnan Kahin as the start of Khnh's ultimate political decline. Due to the intervention of K and Thi, Khnh was now indebted to them, and in an attempt to maintain his power in the face of increasing military opposition, he tried to court support from Buddhist civilian activists, who supported negotiations with the communists to end the Vietnam War. As the Americans were strongly opposed to such policies, relations with Khnh became increasingly strained and he was deposed in February 1965 with US connivance.

The Army of the Republic of Vietnam (ARVN; Vietnamese: Lục quân Việt Nam Cộng hòa; French: Armée de la république du Viêt Nam) were the ground forces of the South Vietnamese military from its inception in 1955 to the Fall of Saigon in April 1975. It is estimated to have suffered 1,394,000 casualties (killed and wounded) during the Vietnam War.The ARVN began as a postcolonial army that was trained by and closely affiliated with the United States and had engaged in conflict since its inception. Several changes occurred throughout its lifetime, initially from a 'blocking-force' to a more modern conventional force using helicopter deployment in combat. During the American intervention, the ARVN was reduced to playing a defensive role with an incomplete modernisation, and transformed again following Vietnamization, it was upgeared, expanded, and reconstructed to fulfill the role of the departing American forces. By 1974, it had become much more effective with foremost counterinsurgency expert and Nixon adviser Robert Thompson noting that Regular Forces were very well-trained and second only to the American and Israeli forces in the Free World and with General Creighton Abrams remarking that 70% of units were on par with the US Army. However, the withdrawal of American forces by Vietnamization meant the armed forces could not effectively fulfill all of the aims of the program and had become completely dependent on U.S. equipment since it was meant to fulfill the departing role of the United States.At the ARVN's peak, an estimated 1 in 9 citizens of South Vietnam were enlisted, and it had become the fourth-largest army in the world composed of Regular Forces and the more voluntary Regional and Village-level militias.Unique in serving a dual military-civilian administrative purpose, in direct competition with the Viet Cong, the ARVN had also become a component of political power and suffered from continual issues of political loyalty appointments, corruption in leadership, factional infighting, and occasional open internal conflict.After the fall of Saigon to North Vietnam's People's Army of Vietnam (PAVN), the ARVN was dissolved. While some high-ranking officers had fled the country to the United States or elsewhere, thousands of former ARVN officers were sent to re-education camps by the communist government of the unified Socialist Republic of Vietnam. Five ARVN generals committed suicide to avoid capture by the PAVN/VC.