There were four countries that were divided during the years after World War II as the result of global Communist strategy: China, Germany, Korea, and Vietnam. Until formal reunification in 1976, Vietnam was split at the 17th parallel of latitude into North Vietnam, with a Communist government, and South Vietnam, with a republican government. Much of Vietnam had been controlled by France for over a century as part of French Indochina.

Following World War II a bloody seven-and-a-half-year struggle raged between Communist Vietnamese and the French for control of the land. Finally a peace conference was held at Geneva, Switzerland, to determine the fate of Indochina. Concluding in July 1954, the conference determined that French rule would be ended in Vietnam and that the country would be temporarily divided politically.

Neighboring Laos and Cambodia, comprising the rest of Indochina, were prohibited from making military alliances. Foreign military bases were barred from their territory and from Vietnam. (See also Cambodia; Laos; Indochina.)

Not long after the 1954 partition, United States military advisers assumed the task of training the South Vietnamese army. At the same time, Ho Chi Minh, president of North Vietnam, pledged to "liberate" South Vietnam.

Communist guerrillas, known as the Viet Cong, infiltrated across the border and by way of Laos in large numbers, supplementing bands of native Communist terrorists in the south. A chief objective of these rebels--who were directly controlled by the Vietminh, North Vietnam's governing faction--was to disrupt South Vietnamese social and economic improvement programs. The assassination of local administrators was one of the ways in which guerrillas sought to bring this about. Guerrilla bands also raided industrial plants, plantations, military installations, and entire villages. Frequently they attacked at night, withdrawing afterward to the security of the forest. Seldom were the South Vietnamese forces able to fight them in the open.

The struggle in Vietnam was never concentrated along a single front. Patches and strips of Communist-held territory spread gradually across the map of South Vietnam. By 1965 much of the coastline and nearly all borderlands had fallen to the rebels. Most of the Mekong Delta, Vietnam's vital rice-growing area, had also been seized.

Rebel gains coincided with the waning popularity of South Vietnam's president, Ngo Dinh Diem. Elected in 1955, Diem enjoyed great popularity at first, but public support, as well as that of military officers and cabinet ministers, gradually disappeared. This stemmed largely from the fact that Diem's brother and closest adviser, Ngo Dinh Nhu, was able to manipulate officers and military units at his discretion. Madame Ngo Dinh Nhu, Diem's bitterly outspoken sister-in-law, also played a unique and important role in arousing the disfavor of Vietnamese and foreigners alike.

In October 1961 President John F. Kennedy sent his military adviser, Gen. Maxwell D. Taylor, to South Vietnam to evaluate that country's economic and military condition. General Taylor reported that infiltration of the Viet Cong from the north was increasing, that South Vietnam's economy had suffered drastically, and that better and more equipment was needed. American aid was stepped up. During the next two years more than 16,000 military advisers were sent to South Vietnam, and some 400 million dollars was provided in military aid alone. For the time being, Viet Cong successes were halted.

A serious setback occurred in May 1963, when President Diem, a Roman Catholic, prohibited the flying of the Buddhist flag. Thousands of Buddhists were arrested, and some were tortured or killed. Buddhist priests publicly burned themselves to death in protest; national morale was badly shaken. The Viet Cong attacked with greater fervor. Casualties and desertions from the South Vietnamese army rose sharply as public displeasure with the Diem regime mounted. In early November, barely three weeks before President Kennedy was killed in Dallas, Diem and Nhu were assassinated. A military junta assumed control. The government remained unstable, however, with a marked absence of popular support.

On Aug. 2, 1964, the United States was drawn further into the conflict when the USS Maddox, a destroyer cruising in the Gulf of Tonkin, was attacked by North Vietnamese patrol boats 30 miles off the coast of North Vietnam. Two days later the Maddox and another destroyer were attacked; two North Vietnamese patrol boats were sunk by return fire. President Lyndon B. Johnson ordered retaliatory air attacks.

The continuing instability of the Vietnamese government made United States assistance more difficult. Coups, attempted coups, or government shake-ups occurred almost monthly. The State Department warned that unless Vietnamese army officers kept out of politics, American aid might be discontinued. Mass demonstrations by Buddhist groups alternated with those of Catholics, depending upon which of these groups was in power at the time.

Terrorist attacks upon American installations in South Vietnam became frequent. These were calculated to discourage the United States into complete withdrawal from Vietnam. Their immediate effect, however, was to increase the tempo of air raids by American aircraft against North Vietnam. Principal targets were highways and bridges. In neighboring Laos, bombers also struck the Ho Chi Minh Trail, an important Viet Cong supply line. United States warships shelled North Vietnamese coastal installations.

In April 1965 President Johnson proposed that "unconditional discussions" be held for a settlement of the conflict. His peace move was ignored by North Vietnam. The North Vietnamese insisted that United States forces first be withdrawn from South Vietnam. They also stipulated that the United Nations must not intervene and that the internal affairs of South Vietnam would have to be settled in accordance with the program of the National Liberation Front, the political arm of the Viet Cong. Johnson maintained that these matters could not be discussed prior to a peace conference. In June he urged the United Nations to seek a solution.

An era of relative stability in South Vietnam's government began in June when a new military regime was installed. The new regime was led by a ten-man military junta, which called itself the National Leadership Committee. Air Force Commander Vice- Marshal Nguyen Cao Ky, a member of the council, was named premier.

Ky's first crisis in office followed his dismissal of Lieut. Gen. Nguyen Chanh Thi in March 1966 from the military council and from his post as a regional army commander. Thi had established himself as virtual warlord of several provinces in northern South Vietnam. He had also aligned himself with politically powerful Buddhists, including Thich Tri Quang. When followers of General Thi publicly protested his dismissal, Tri Quang encouraged further antigovernment demonstrations. The Buddhists demanded that civilians be represented on the governing council and that elections be held for a national assembly.

Civil war threatened as fighting erupted between government forces and troops loyal to Thi. Riots instigated by the Buddhists, notably Tri Quang, broke out in Saigon, Hue, and Da Nang. Again, as in 1963 Buddhists publicly burned themselves to death. In April Premier Ky acceded to most of the Buddhist demands; elections were scheduled for later in the year. The unrest continued, however, as militant Buddhists called for Ky's resignation. Meanwhile government troops won back control of the cities which had been taken over by Thi's followers. By mid-1966 the rioting had also subsided.

During 1965 the United States became even more deeply committed to South Vietnam's struggle for freedom. In February it was officially revealed that planes raiding North Vietnam were being flown by American personnel. In June it was acknowledged that United States troops were engaged in combat with the Viet Cong. By midyear the size of the United States force in South Vietnam exceeded 50,000 troops, having doubled in less than six months. Although contingents had also arrived from South Korea, Australia, and New Zealand, the military situation in South Vietnam continued to deteriorate. Military observers theorized that 1965 was the year scheduled by the Communists for total victory. With the approach of the summer rainy season and an anticipated Viet Cong offensive, Ky asked for more American ground forces. Between July and November a fighting force of an additional 100,000 men was transferred from military bases in the United States to Vietnam.

The first major American victory took place in August at Chu Lai, where more than 5,000 United States troops defeated an estimated 2,000 Viet Cong. In November American forces won a decisive victory over a large North Vietnamese force in the Ia Drang Valley. It was the first time that a major Viet Cong or North Vietnamese force had abandoned hit-and-run guerrilla tactics for open combat. Ia Drang was the bloodiest battle of the war to that date.

In January 1966 some 20,000 American, South Vietnamese, and South Korean troops encircled four enemy regiments south of Da Nang. A successful allied sweep through the central coastal province of Binh Dinh took place in the spring.

In February 1965 United States bombers attacked North Vietnam in retaliation for a Viet Cong raid on the United States helicopter base at Plei Ku. The Viet Cong bombing raids continued, however.

In May the air strikes against the North were suspended for five days, following President Johnson's invitation in April to "unconditional discussions" of peace. The raids were again suspended in late December 1965 and throughout January 1966 as a so-called "peace offensive" was launched by President Johnson and other world leaders. The North Vietnamese failed to respond to these overtures.

In June 1966 United States bombers made their first attack on the industrial outskirts of North Vietnam's two largest cities--Hanoi, the capital, and Haiphong, the chief port. Subsequent American bombing raids were made on these as well as other industrial centers and on MiG air bases in North Vietnam.

United States forces--increased from 190,000 in January 1966 to more than 500,000 by early 1968--used "search-and-destroy" tactics to expel National Liberation Front (NLF) forces from the South. In 1967 and 1968, American troops raided NLF troop concentrations in the demilitarized zone.

In January 1968 the NLF launched a large-scale offensive throughout the South during Tet, the Vietnamese Lunar New Year holiday. The targets included about 30 provincial capitals.

On March 31 President Johnson--faced with increasing antiwar sentiment--announced a halt in all bombing north of the 20th parallel and offered to negotiate for peace with North Vietnam. Peace talks began in Paris in May, but were quickly deadlocked. After the United States stopped bombing North Vietnam in early November, the North Vietnamese agreed not to escalate the war. In January 1969 South Vietnam and the NLF joined the talks.

On April 29, 1970, American and South Vietnamese ground forces began an assault on North Vietnamese and NLF sanctuaries in Cambodia. Months later, similar action was taken by the South Vietnamese on targets in Cambodia and Laos in 1971. (In 1973 the United States government reluctantly admitted that it had conducted secret bombing missions inside Cambodia in 1969, and in Laos in 1970.) American troop withdrawals, which had begun in the summer of 1969, left fewer than 200,000 Americans in South Vietnam at the end of 1971.

In April 1972 the United States bombed civilian dwellings and military targets in the cities of Hanoi and Haiphong. In May of that year, in response to a drive by the North Vietnamese forces into the South, President Richard M. Nixon ordered the mining of harbors off North Vietnam. Both the bombing and the mining provoked sustained antiwar protests within the United States.

On Jan. 27, 1973, a cease-fire was signed in Paris by the United States, South Vietnam, North Vietnam, and the Provisional Revolutionary Government of the NLF. A Four-Party Joint Military Commission was set up to implement such provisions as the withdrawal of foreign troops and the release of prisoners. An International Commission of Control and Supervision was established to oversee the cease-fire.

United States ground troops left Vietnam by the end of March 1973. Fighting continued, however, as the North and the South accused each other of truce violations. A second cease-fire was signed in June, but the hostilities continued through 1974.

The ultimate fall of South Vietnam began with the capture of Phuoc Long Province in January 1975. Soon more inland provinces were under North Vietnamese control and the major coastal cities had fallen, with little resistance from Southern troops. The war in Cambodia ended on April 16, and the South surrendered on April 30, 1975, as enemy troops entered Saigon. (See also Vietnam; Ho Chi Minh.)