During the Vietnam War, the ROKMC dispatched the Cheongryeong ('Blue Dragon') brigade to the Republic of Vietnam.

At the request of the United States, President Park Chung Hee of the Republic of Korea agreed to send military units into Vietnam, despite opposition from both the Assembly and the public. In exchange, the United States agreed to provide additional military funds to Korea to modernize its armed forces, totaling about a billion dollars.

The Republic of Korea Army units' Tactical Area of Responsibility were the southern half of the I Corps. The ROK Marine Corps units were deployed with the I Corps alongside US Marines.

Under an arrangement with the USMC, air assets would be provided to the brigade and assigned the same priority for available aircraft as are American units. A team of experts from Subunit One, 1st ANGLICO was dispatched and charged with the mission of keeping an air umbrella over the Blue Dragon Brigade in and out of the field. A two man fire control team was assigned to each ROKMC infantry company at all times.

Initially, the AK-47-equipped Vietcong and NVA outgunned Korean soldiers, since they were armed with World War II-era weaponry (M1 Garand and M1 carbine). However, they soon received more modern weapons from the United States military such as the M16 rifle.

The three main units deployed to Vietnam were the Marine Corps’ (Blue Dragon) Brigade, ROKA Capital Division and the White Horse Division. Various ROK special forces units were also deployed.

Most of the operations never exceeded battalion-size, but they also conducted divisional size operations. Before conducting missions, the South Korean marines laid out their plans much more carefully than their allies, with greater fire discipline, effective use of fire support, and better coordination of sub-units. They also had to their favor the distinguished combat leadership of the company and platoon commanders. During village searches, ROK soldiers would subject the settlement to a series of detailed sweeps while interrogating subjects on the spot. By comparison, American units tended to favor a single sweep followed by a removal of all civilians for screening. Such a painstaking approach certainly paid dividends in terms of weapons seizures and reduced VC activity in ROK areas. Koreans quickly learned pidgin Vietnamese language; for fear that most Vietnamese translators were spies for Vietcong and NVA. Koreans also had better field intelligence than their American counterparts. Koreans conducted counterinsurgency operations so well that American commanders felt that the Korean TAOR was the safest. This was further supported when Vietcong documents captured after the Tet Offensive warned their compatriots to never engage Koreans until full victory was certain. In fact, it was often that the NVA and Vietcong were ambushed by Koreans and not vice versa.

Apparently the ROK Marines were experts at locating enemy weapons caches. The official U.S. report on South Korean participation in Vietnam, entitled "Vietnam Studies: Allied Participation in Vietnam," states that "The enemy feared the Koreans both for their tactical innovations and for the soldiers' tenacity. It is of more than passing interest to note that there never was an American unit in Vietnam which was able to 'smell out' small arms like the Koreans. The Koreans might not suffer many casualties, might not get too many of the enemy on an operation, but when they brought in seventy-five or a hundred weapons, the Americans wondered where in the world they got them. They appeared to have a natural nose for picking up enemy weapons that were, as far as the enemy thought, securely cached away. Considered opinion was that it was good the Koreans were 'friendlies.'"

One of the most notable operations during the Vietnam War was The Battle of Tra Binh Dong in which just under 300 marines successfully defended their base against over 2,400 Viet Cong. Another notable operation is Operation Flying Tiger in early January of 1966; here, the Koreans accounted for 192 Viet Cong killed as against only eleven Koreans.

The U.S. Army manual on Korean participation in Vietnam also states that "[t]he Koreans were thorough in their planning and deliberate in their execution of a plan. They usually surrounded an area by stealth and quick movement. While the count of enemy killed was probably no greater proportionately than that of similar US combat units, the thoroughness with which the Koreans searched any area they fought in was attested to by the fact that the Koreans usually came out with a much higher weaponry count than US troops engaged in similar actions."

A total of 320,000 Koreans served in Vietnam, with a peak strength (of any given time) at around 48,000. About 4,000 were killed. The Korean forces in Vietnam were frequently able to amass a kill ratio of about 25:1 compared to the average American kill ratio of less than 9:1. The U.S Army manual on Korean participation in Vietnam states that" an analysis of an action by Capital Division forces during the period 23–29 January 1968 clearly illustrates the Korean technique. After contact with an enemy force near Phu Cat, the Koreans reacting swiftly...deployed six companies in an encircling maneuver and trapped the enemy force in their cordon. The Korean troops gradually tightened the circle, fighting the enemy during the day and maintaining their tight cordon at night, thus preventing the enemy's escape. At the conclusion of the sixth day of fighting, 278 NVA had been KIA with the loss of just 11 Koreans, a kill ratio of 25.3 to 1. Later in 1968 a Korean 9th Division operation titled Baek Ma 9 (Korean for "white horse," after the White Horse Division) commenced on 11 October and ended on 4 November with 382 enemy soldiers killed and the NVA 7th Battalion, 18th Regiment, rendered ineffective. During this operation, on 25 October, the eighteenth anniversary of the Division, 204 of the enemy were killed without the loss of a single Korean soldier."

The official U.S. military record on South Korean participation in the Vietnam war reads, "In summary, it appears that Korean operations in Vietnam were highly professional, well planned, and thoroughly executed; limited in size and scope, especially in view of assets made available; generally unilateral and within the Korean tactical area of responsibility; subject to domestic political considerations; and highly successful in terms of kill ratio."

In 1950, the People's Republic of China extended diplomatic recognition to the Viet Minh's Democratic Republic of Vietnam and sent weapons, as well as military advisors led by Luo Guibo to assist the Viet Minh in its war with the French. The first draft of the 1954 Geneva Accords was negotiated by French Prime Minister Pierre Mendès France and Chinese Premier Zhou Enlai who, fearing U.S. intervention, urged the Viet Minh to accept a partition at the 17th parallel.

China's ability to aid the Viet Minh declined when Soviet aid to China was reduced following the end of the Korean War in 1953. Moreover, a divided Vietnam posed less of a threat to China. China provided material and technical support to the Vietnamese communists worth hundreds of millions of dollars. Chinese-supplied rice allowed North Vietnam to pull military-age men from the paddies and imposed a universal draft beginning in 1960.

In the summer of 1962, Mao Zedong agreed to supply Hanoi with 90,000 rifles and guns free of charge. Starting in 1965, China sent anti-aircraft units and engineering battalions to North Vietnam to repair the damage caused by American bombing, rebuild roads and railroads, and to perform other engineering works. This freed North Vietnamese army units for combat in the South.

Sino-Soviet relations soured after the Soviets invaded Czechoslovakia in August 1968. In October, the Chinese demanded North Vietnam cut relations with Moscow, but Hanoi refused. The Chinese began to withdraw in November 1968 in preparation for a clash with the Soviets, which occurred at Zhenbao Island in March 1969. The Chinese also began financing the Khmer Rouge as a counterweight to the Vietnamese communists at this time. China's withdrawal from Vietnam was completed in July 1970.

The Khmer Rouge launched ferocious raids into Vietnam in 1975–1978. Vietnam responded with an invasion that toppled the Khmer Rouge. In response, China launched a brief, punitive invasion of Vietnam in 1979.

The Fall of Saigon was the capture of Saigon, the capital of South Vietnam, by the North Vietnamese Army on April 30, 1975. The event marked the end of the Vietnam War and the start of a transition period leading to the formal reunification of Vietnam under communist rule.

North Vietnamese forces under the command of the Senior General Văn Tiến Dũng began their final attack on Saigon, which was commanded by General Nguyen Van Toan on April 29, with a heavy artillery bombardment. By the afternoon of the next day, North Vietnamese troops had occupied the important points within the city and raised their flag over the South Vietnamese presidential palace. South Vietnam capitulated shortly after. The city was renamed Ho Chi Minh City, after communist leader Ho Chi Minh. The fall of the city was preceded by the evacuation of almost all the American civilian and military personnel in Saigon, along with tens of thousands of South Vietnamese civilians associated with the southern regime. The evacuation culminated in Operation Frequent Wind, which was the largest helicopter evacuation in history. In addition to the flight of refugees, the end of the war and institution of new rules by the communists contributed to a decline in the population of the city.

Chaos, unrest, and panic broke out as hysterical South Vietnamese officials and civilians scrambled to leave Saigon. Martial law was declared. American helicopters began evacuating South Vietnamese, U.S., and foreign nationals from various parts of the city and from the U.S. embassy compound. Operation Frequent Wind had been delayed until the last possible moment, because of U.S. Ambassador Graham Martin's belief that Saigon could be held and that a political settlement could be reached.

Schlesinger announced early in the morning of 29 April 1975 the evacuation from Saigon by helicopter of the last U.S. diplomatic, military, and civilian personnel. Frequent Wind was arguably the largest helicopter evacuation in history. It began on 29 April, in an atmosphere of desperation, as hysterical crowds of Vietnamese vied for limited space. Martin pleaded with Washington to dispatch $700 million in emergency aid to bolster the regime and help it mobilize fresh military reserves. But American public opinion had soured on this conflict.

In the United States, South Vietnam was perceived as doomed. President Gerald Ford had given a televised speech on 23 April, declaring an end to the Vietnam War and all U.S. aid. Frequent Wind continued around the clock, as North Vietnamese tanks breached defenses on the outskirts of Saigon. In the early morning hours of 30 April, the last U.S. Marines evacuated the embassy by helicopter, as civilians swamped the perimeter and poured into the grounds. Many of them had been employed by the Americans and were left to their fate.

On 30 April 1975, VPA troops overcame all resistance, quickly capturing key buildings and installations. A tank crashed through the gates of the Independence Palace, and at 11:30 a.m. local time the NLF flag was raised above it. President Duong Van Minh, who had succeeded Huong two days earlier, surrendered.

The Communists had attained their goal, but the cost of victory was high. By war's end, the Vietnamese had been fighting foreign involvement or occupation (primarily by the French, Chinese, Japanese, British, and American governments) for 116 years.