Hanoi moved rapidly to unify the country. The Provisional Revolutionary Gov- ernment of South Vietnam was pushed aside and administrators were sent from  the north to establish the new regime in the south. Many Second Republic officials were killed and hundreds of thousands of people were sent to concentration camps, ostensibly to re-educate them to live in a socialist society. A system of registering the population was instituted to ensure that those whose families had  supported the Second Republic were penalized by denial of employment, educa- tion, and food rations. An ambitious plan for economic development was initiated,  but within three years the country was facing political, economic, and diplomatic failures. These failures became parts of a crisis that led to a new war. The harsh official attitude toward the defeated population squandered a potential reservoir of good will among many southerners who were ready to turn their backs on the past and to contribute to building a new united country. The Hanoi government even marginalized southern communists. Many people from urban areas were relocated with a minimum of preparation in relatively remote “new economic zones” in rural areas. Large numbers of these people surreptitiously returned to the cities. Efforts to collectivize southern agriculture were stymied by the resistance of the rural population. In the shadow of a new war, the Hanoi leaders rushed to gain control of the south and to integrate its resources into its militarized economy. The strategic situation after the withdrawal of American power shifted rapidly as China and the Soviet Union competed for influence in Southeast Asia. The pressure point of this confrontation was the Cambodian–Vietnamese border, a border that, while drawn by French colonial administrators in the 1930s, was very close to the border that existed prior to the French arrival in the nineteenth century. This border was based on the Vietnamese acquisition of formerly Cambodian territories in the seventeenth and eighteenth centuries. While it was considered to be a satisfactory border by Vietnamese authorities, Cambodian nationalists were unreconciled to the loss of the lower Mekong plain, and this was particularly true of the Cambodian communists who gained control of Phnom Penh in 1975 under the leadership of Saloth Sar (1925–1998), also known as Pol Pot. Added to the sense of a historical grievance was the strong resistance of Pol Pot to what he understood as the threat of Vietnam dominating Cambodia in the same way that it dominated Laos. Some Cambodian communists, particularly those in the eastern provinces along the Vietnamese border, were willing to collaborate with the Vietnamese and even to defer to Vietnamese leadership. Pol Pot, full of nationalist fervor and feeling surrounded by enemies, was eager to eliminate what he viewed as colonial residue, whether French, Vietnamese, or Cambodian. He initiated a homicidal policy against urbanites, people with education, and the people of the eastern provinces. By 1977, Pol Pot, with the benefit of Chinese economic and military assistance, initiated attacks across the Vietnamese border to eliminate the Vietnamese population in areas that Phnom Penh claimed as Cambodian. In response, Vietnam briefly campaigned into Cambodia in late 1977. Between two and three hundred thousand Cambodians fled their country and followed the Vietnamese  withdrawal back into Vietnam where they constituted a large refugee popula- tion. Hanoi’s efforts to negotiate a settlement of the border issue were rejected by  Phnom Penh, and it became apparent that Cambodian intransigence on the border issue was tacitly supported by China. The next phase of sliding into war focused on the ethnic Chinese population in Vietnam. This population had developed differently in northern and southern Vietnam. Southern Chinese had been forced to take Vietnamese citizenship in the late 1950s. In the north, however, the relatively smaller Chinese population had been accorded a special status: it was allowed to retain Chinese citizenship with its privilege of travel to China and was exempted from Vietnamese military conscription and from certain tax liabilities. Chinese in the north were experts  in the unofficial Sino-Vietnamese cross-border trade and in the south had accu- mulated wealth from their business skills and international contacts. By early  1978, Vietnamese authorities perceived the Chinese communities as not only threats to their plans for a socialist economy but also a fifth column allied with China in the armed confrontation that was rapidly materializing. When the Vietnamese acted to confiscate the property of Chinese in the south and to force  the southern Chinese population into the socialist economy, thousands of south- ern Chinese fled from the country by sea. At the same time, Hanoi endeavored to  restrict the Chinese population in the north, fearing their vulnerability to being manipulated by China. When China announced that Vietnam was persecuting the Chinese and that it was sending ships to rescue them, there was a stampede of northern Chinese to the Sino-Vietnamese border. By the summer of 1978, the prospect of a Sino-Vietnamese war loomed over the region as China continued to build up the Cambodian army and concentrated troops along the Sino-Vietnamese border. The Vietnamese economy was in shambles with confiscation of private property and the penalization of people with wealth in the south, with the ruin of southern agriculture by the failed collectivization effort, and with plans for industrial development in the north stillborn by lack of investment and the return of wartime priorities.

Added to the turmoil in domestic affairs and in relations with China and Cambodia, Vietnam fell afoul of the Cold War shift from China and the Soviet Union against the US to China and the US against the Soviet Union. Failing in negotiations to normalize relations with the US, Vietnam signed a strategic treaty with the Soviet Union and made plans to strike Cambodia before China could act, thereby initiating a war that for the next ten years kept Vietnam encircled by enemies with a thin lifeline to the Soviet Bloc countries.

After organizing the semblance of an allied Cambodian government from among the Khmer refugees, Vietnam invaded Cambodia at the end of 1978 and within days had defeated the Cambodian army and sent Pol Pot and his associates fleeing to the Thai border. China, having just normalized relations with the US and eager to demonstrate its strategic value as an anti-Soviet ally, briefly invaded Vietnamese border provinces in early 1979 and then withdrew  after destroying the economic and administrative infrastructure there. There- after, Sino-Vietnamese hostilities continued with cross-border shelling and raids  while the main arena of the war was in Cambodia, where Vietnam supervised the establishment of a Cambodian army and government.

Contesting Vietnamese ascendancy in Cambodia were three Cambodian groups operating from bases along the Thai border with the logistical support of the Thai army. China provided supplies primarily to Pol Pot. The neighboring countries that had allied with the US in the 1960s, which included Thailand, Singapore, Malaysia, Indonesia, and the Philippines (the five ASEAN countries), mainly supported a royalist group led by Sihanouk. The US gave support to a third group espousing parliamentary democracy led by Son Sann (1911–2000), a veteran politician who had been active in politics since the 1940s. Supervised by China, the US, and the ASEAN countries, the three groups were diplomatically organized, presented, and acknowledged in the United Nations as the legitimate coalition government of Cambodia, thereby preventing the government formed in Phnom Penh, supported by Vietnam and the Soviet Bloc countries, from receiving UN recognition.

The three anti-Vietnamese Cambodian groups established bases just inside the Cambodian border from where they launched guerrilla operations. During the 1984–1985 dry season, Vietnamese forces attacked and destroyed all of these bases. Thereafter, Vietnam began to withdraw its army back to Vietnam, handing responsibility for defending the country to its client government in Cambodia, which from 1985 was led by Hun Sen (b. 1952), a former follower of Pol Pot who had defected to Vietnam in 1977.

The collapse of the Soviet Union removed the rationale of the war. Vietnam accordingly completed its withdrawal from Cambodia in 1989. In the early 1990s, the UN sponsored a ceasefire and elections in Cambodia, which led to a brief coalition between the royalists and Hun Sen, yet Hun Sen and his followers continued to dominate Cambodian politics well into the twenty-first century. This superficially appeared to vindicate Vietnam’s war aims. However, regional politics shifted sharply in the 1990s with Vietnam joining ASEAN and making peace with China. Furthermore, the price paid by Vietnam for this war was very high, bringing unprecedented economic distress. It also contributed to an exodus of people fleeing the country by sea, sojourning in regional refugee camps, and emigrating to foreign lands.

In the early years of the Sino-Khmer War, deepening poverty forced Hanoi to acquiesce in a new system of agriculture that restored some incentive for private initiative with contracts for farmers to supply the state with specified amounts of produce and allowing anything beyond that to be freely marketed for private profit. This somewhat alleviated the food supply and led to relative well being in the countryside. During the 1980s, villagers in northern Vietnam began to invest their private earnings in building brick homes to replace their thatched wooden dwellings. Urban populations, however, suffered from a lack of income, a deteriorating infrastructure, a scarcity of consumer goods, and hunger.

The death of Le Duan in the spring of 1986 made possible a shift in domestic policy. Truong Chinh presided over the party for six months during which Nguyen Van Linh (1915–1998) rode the pressures for reform to replace him. Nguyen Van Linh was originally from Hanoi, had joined the party in the 1930s, and spent several years in French prisons. In 1975, he became the leader of the party in the south where he had been assigned since the early 1960s. By the mid 1980s, he was known to be at odds with Le Duan over economic and cultural policy. He favored a loosening of state control over markets, religious and cultural activities, and journalism. During his years as head of the party, from late 1986 to mid 1991, he nurtured a younger generation of party leaders and initiated what became known as the doi moi policy, literally “to change to the new,” commonly rendered in English as “renovation.” As the Sino-Khmer War  ended and the Soviet Bloc disappeared, he restored trade with China and encour- aged foreign investment from Japan, South Korea, Taiwan, Singapore, and other  countries. He invited journalists to report on corruption and abuse, allowed publication of literary works critical of party policies, and encouraged the restoration of temples and local festivals.

One aspect of the renovation policy was an effort to create a sense of continu- ity with pre-revolutionary culture by cultivating new versions of traditional art,  music, theater, village festivals, and religious pilgrimage sites. The rebuilding and repair of temples became possible with contributions from a rising class of businesswomen who worked in the urban markets. Many temples in northern Vietnam had been neglected and not a few were even plundered and destroyed by greedy or fanatical officials. Perhaps the most notorious example is the many lavishly furnished temples on Mount Yen Tu, around 125 kilometers east of Hanoi, which dated to the Tran dynasty and were a major pilgrimage destination for centuries. By the time of the renovation policy, they had all been stripped of valuables and burned down under the supervision of local officials. In the early 1990s, a monk returned to the mountain and, with government approbation, began to rebuild one of the temples with contributions of pilgrims. Within a few years, the government had built a new road to the foot of the mountain and a welcoming center for the growing number of pilgrims.

At the party congress in 1991, Nguyen Van Linh stepped down, ostensibly because of poor health, and was replaced by Do Muoi (b. 1917). Do Muoi was born near Hanoi, had joined the party in his youth, and had made his career in the state bureaucracy. During his six years at the head of the party, the doi moi policy was basically preserved. At the same time, there was a stronger emphasis upon internal security measures to affirm the party’s control over public opinion and political activity. In 1997, Do Muoi was succeeded by his protégé Le Kha Phieu (b. 1931). Le Kha Phieu had made his career in the military and was critical  of corruption and factionalism in the party. However, his anti-corruption cam- paigns united virtually all the party factions against him, and, in 2001, he was  forced to retire. Nong Duc Manh (b. 1940), a forestry expert from the mountains north of Hanoi rumored to be a son of Ho Chi Minh, replaced him and remained head of the party for ten years with a policy of economic development and strong party control modeled on the example of China.

One of Le Kha Phieu’s unpopular acts was completing a treaty with China that demarcated the land border and the Gulf of Tonkin sea border. Many Vietnamese considered that this treaty conceded too much to China and represented a proffering of homage to the big northern neighbor. However, with communist parties losing power in many countries during the 1990s, the Chinese and Vietnamese parties gradually built a new version of the close relationship that had existed between the two countries for centuries. But new conditions in the twenty-first century placed limits on this relationship and created a contradiction for party leaders.

On the one hand, by the first decade of the twenty-first century, the Vietnam- ese ruling party’s ability to maintain power depended upon the continued success  of the Chinese ruling party to control China. Any political change in China that displaced the Chinese party would have made it very difficult for the Vietnamese  party to avoid political change as well. A close and mutually supportive relation- ship between the two parties helped to sustain the regime in Vietnam.

On the other hand, the rise of popular nationalism in both countries exacer- bated the underlying tension in the relationship between a China seeking regional  dominance and a Vietnam determined to resist subordination. This tension was concretely expressed in the growing dispute over the islands in the South China Sea. The Hoang Sa (Paracel) archipelago had been inherited from France and occupied by South Vietnam until it was seized by China in 1974. The Truong Sa (Spratley) archipelago was claimed and partly occupied by China but parts of it were also claimed and occupied by Vietnam, the Philippines, and other countries. Hanoi appeared to acknowledge Chinese sovereignty over the islands in the late 1950s when it was dependent upon China for its policy of taking over the south, but from 1975 the Vietnamese government forcefully announced its claim to the islands.

After the Sino-Khmer War, Vietnamese foreign policy experts debated whether to follow China and to prosper as a junior regional partner in what was imagined as an inevitable Chinese hegemony over eastern and southeastern Asia, or whether to follow a multi-directional policy aimed to maximize anti-Chinese leverage in cooperation with the ASEAN countries, Japan, and the US. This debate continued into the twenty-first century, fueled by the island dispute and the fear that China would eventually enforce its claims unless the US remained a balancing presence in the region. At the beginning of the twenty-first century, having weathered the storms of French colonialism, the Japanese Empire, and both phases of the Cold War, the Vietnamese faced the prospect of returning to a Sinic world order, unsure about how feasible for the long term a multi-lateral foreign policy option might be. In general, northerners view such a prospect with less dismay than do southerners.