The Vietnamese invasion of Cambodia in December 1978, the overthrow of the Khmer Rouge and the establishment of the People's Republic of Kampuchea, the Sino-Vietnamese war of February to March 1979, and the end of the conflict in Indochina

Needs a clear judgment, dated evidence, and analysis of both campaigns.

Thesis

The Vietnamese invasion of Cambodia in December 1978 ended the Khmer Rouge regime and the Sino-Vietnamese war of February to March 1979 ended the active conflict between the major Indochinese and regional powers, but the Cambodian struggle continued through the 1980s and a final settlement came only in 1991.

Background

Khmer Rouge raids into Vietnam from 1977 (Ba Chuc massacre 18 April 1978, around 3,000 Vietnamese civilians killed). Hanoi signed a Treaty of Friendship with Moscow on 3 November 1978.

Invasion

Vietnam invaded with around 150,000 troops on 25 December 1978. The Kampuchean United Front under Heng Samrin (formed 2 December 1978) provided cover. Phnom Penh fell on 7 January 1979.

PRK

The People's Republic of Kampuchea was proclaimed on 8 January 1979 under Heng Samrin and Hun Sen. Vietnam stationed around 200,000 troops in Cambodia until 1989. The UN seat stayed with the Khmer Rouge.

Sino-Vietnamese war

China invaded northern Vietnam on 17 February 1979 with around 250,000 PLA troops along a 480-kilometre front, reaching Lang Son, Lao Cai, and Cao Bang. PLA withdrew on 16 March. Casualties were heavy (perhaps 26,000 PLA, 30,000 PAVN killed).

Aftermath

The Cambodian civil war continued through the 1980s. The Paris Peace Agreements of 23 October 1991 ended it. The Khmer Rouge dissolved in 1999.

Markers reward 25 December 1978, 7 January 1979, and 17 February 1979.

A 3-mark "outline" wants three distinct, dated provocations, each in a sentence.

Territorial claims and raids

From 1977 Democratic Kampuchea claimed the Mekong Delta and launched cross-border raids into An Giang, Tay Ninh and Kien Giang Provinces.

The Ba Chuc massacre

On 18 April 1978 Khmer Rouge units killed around 3,157 Vietnamese civilians (only two survivors).

Ethnic cleansing of Vietnamese

Ethnic Vietnamese inside Cambodia were expelled or killed; around 150,000 fled in 1977 to 1978, and the May 1978 Eastern Zone purge drove future PRK leaders (Heng Samrin, Hun Sen) into exile in Vietnam.

Marking criteria

1 mark each for three distinct, correctly dated provocations; do not narrate the invasion itself.

A 4-mark "explain" needs a cause-and-effect chain with specific detail.

The strategic problem

China backed Pol Pot and was normalising relations with the United States (announced 15 December 1978, effective 1 January 1979), so Hanoi risked a Chinese response if it moved against the Khmer Rouge.

The treaty

The Treaty of Friendship and Cooperation, signed in Moscow on 3 November 1978, obliged the parties to consult if either were attacked - an explicit Soviet umbrella.

The effect

Reassured against Chinese escalation, the Politburo committed to invasion; the Kampuchean United Front (2 December 1978) supplied political cover, and the attack followed on 25 December 1978.

Marking criteria

1 mark for the China/USSR strategic context; 1 mark for dating the treaty; 1 mark for its consultation obligation; 1 mark for linking it to the decision to invade.

A 5-mark "explain ... using the source" wants the source decoded, then linked to own knowledge.

Decode the source

The report captures the speed of the conventional campaign (Phnom Penh fell on 7 January 1979, 13 days after the 25 December invasion), the immediate proclamation of a new government, and its dependence on Vietnam and isolation abroad.

Own knowledge

The People's Republic of Kampuchea was proclaimed on 8 January 1979 under Heng Samrin, with Vietnamese advisers running the ministries and around 200,000 PAVN troops stationed in the country. The PRK reopened schools, restored markets and a limited Buddhism, and preserved S-21 as the Tuol Sleng museum.

The isolation

As the source notes, the PRK was not recognised; the UN kept the Cambodian seat with the Khmer Rouge year after year, and ASEAN, the US and China backed the resistance.

Marking criteria

1 mark for decoding the source (speed, dependence, isolation); 1-2 marks for own knowledge on the PRK's founding and Vietnamese control; 1 mark for the non-recognition/UN seat point; 1 mark for a coherent explanation.

A 6-mark "assess the usefulness" rewards origin/perspective plus own knowledge, ending in a judgement.

Perspective

Source B is a military historian's analysis (the line taken by Edward O'Dowd and Xiaoming Zhang) stressing PLA backwardness - useful because it explains why a far larger Chinese force took such heavy losses in three weeks.

Corroboration from own knowledge

It fits the record: around 250,000 PLA in 29 divisions attacked on 17 February 1979 without close air support; they took Cao Bang, Lao Cai (24 February) and Lang Son (5 March) but suffered perhaps 26,000 killed, against a PAVN northern garrison that was largely militia because the regulars were in Cambodia.

Limitation

By focusing on tactics it can understate the war's strategic logic - Deng's "lesson" to deter Vietnam, signal to the USSR, and pressure Hanoi over Cambodia - and the Soviet treaty restraint that limited Chinese aims.

Judgement

Highly useful for explaining the PLA's costly performance and its modernisation lesson, but it must be read alongside the strategic and diplomatic context to explain why the war was fought at all.

Marking criteria

1 mark for identifying the military-history perspective; 2 marks for own knowledge corroborating it (dates, scale, casualties, militia garrison); 1-2 marks for a limitation (strategic/diplomatic context); 1 mark for a judgement on usefulness.

This is an extended-response/essay. Markers reward a sustained, evidence-based argument that addresses the question directly and weaves in historiography - not a narrative.

Band-6 PLAN

• Thesis. The events of 1978 to 1979 ended the ACTIVE phase of the Indochina conflict - the Vietnamese invasion destroyed the Khmer Rouge state and the Sino-Vietnamese war closed direct fighting between the major powers - but they did not end the Cambodian conflict itself, which ran on until the Paris Peace Agreements of 1991. Their significance is real but bounded.
• Argument 1 - The invasion ended the Khmer Rouge regime. Provoked by border raids (Ba Chuc, 18 April 1978) and shielded by the Soviet treaty (3 November 1978), Vietnam's 150,000 troops took Phnom Penh on 7 January 1979 and installed the PRK under Heng Samrin (8 January). This ended Democratic Kampuchea as a governing state - a decisive turning point.
• Argument 2 - The Sino-Vietnamese war closed the great-power dimension. China's punitive invasion (17 February to 16 March 1979, around 250,000 PLA) was the last conventional clash of the conflict; both sides claimed victory, but it ended without altering the Cambodian outcome and the powers disengaged from direct fighting.
• Argument 3 - But the conflict did NOT end in 1979. The Khmer Rouge survived in the Cardamom Mountains and the Thai border; the CGDK (22 June 1982) fought on with US, Chinese and Thai backing; the UN seat stayed with the Khmer Rouge; Vietnam occupied Cambodia until September 1989. The conflict ended only with the Paris Peace Agreements (23 October 1991) and UNTAC.
• Historiography. Stephen Morris (Why Vietnam Invaded Cambodia, 1999) reads the invasion as security-driven; Ben Kiernan (How Pol Pot Came to Power, 1985) foregrounds its anti-genocide effect amid mixed motives; Edward O'Dowd (Chinese Military Strategy in the Third Indochina War, 2007) treats the Chinese war as a costly demonstration of PLA limits rather than a strategic success.
• Judgement. Highly significant as the END of the active, state-on-state phase and of the Khmer Rouge in power, but the dot point's "end of the conflict" is only fully reached in 1991; 1979 is the decisive turning point, not the terminus.

MODEL PARAGRAPH (Argument 3)

The events of 1979 are best read as a decisive turning point rather than the end of the conflict, because the Cambodian war they reshaped ran on for more than a decade. Although Vietnam destroyed Democratic Kampuchea as a state and installed the People's Republic of Kampuchea on 8 January 1979, the Khmer Rouge leadership escaped with some 30,000 to 40,000 fighters into the Cardamom Mountains and the Thai border zone, where Thai, Chinese and covert US support kept them in the field. The Coalition Government of Democratic Kampuchea, formed on 22 June 1982, held the Cambodian seat at the United Nations year after year, so the very regime Vietnam had overthrown remained the internationally recognised government while around 200,000 Vietnamese troops occupied the country until September 1989. Only the Paris Peace Agreements of 23 October 1991, brokered by the Security Council's Permanent Five, and the UNTAC administration that followed, brought the conflict to a formal close. As Evan Gottesman shows in Cambodia after the Khmer Rouge (2003), the PRK governed a country still at war; 1979 ended a regime and a phase, not the conflict.

Marker's note. A band-6 response keeps "significance" and "end of the conflict" in view throughout, distinguishing the end of the ACTIVE phase (1979) from the formal settlement (1991), anchors every claim in dated evidence (25 December 1978, 7 January 1979, 17 February 1979, 23 October 1991), and sets at least two historians in genuine tension rather than name-dropping. Narrating the invasion without weighing how far it actually "ended" the conflict caps the response in the middle bands.

This is an extended-response/essay. Markers reward a sustained, evidence-based argument that addresses the view directly and weaves in historiography - not a narrative.

Band-6 PLAN

• Thesis. Vietnam invaded chiefly for SECURITY - to end Khmer Rouge border raids and break Chinese encirclement - and the humanitarian outcome of ending the genocide, though real, was a consequence Hanoi claimed afterwards rather than the driving motive. The view is largely correct, but motives were mixed.
• Argument 1 - Security as the driving motive. The trigger was the Khmer Rouge threat: territorial claims to the Mekong Delta, raids into An Giang and Tay Ninh, and the Ba Chuc massacre (18 April 1978, around 3,157 dead). The 3 November 1978 Soviet treaty was a defensive hedge against China, showing Hanoi's strategic, not humanitarian, calculus.
• Argument 2 - The geopolitical dimension. Vietnam acted to break a Chinese-backed encirclement (Beijing armed Pol Pot while normalising with Washington). The PRK and the Kampuchean United Front gave the invasion a Cambodian face, but the aim was a secure, friendly western flank.
• Argument 3 - The humanitarian counter-case (and its limits). The invasion did end the genocide, and Hanoi stressed this for legitimacy. But it acted only when its OWN security was threatened, not during the worst killing of 1975 to 1977, and it then occupied Cambodia for a decade - hard to square with a primarily humanitarian motive.
• Historiography. Stephen Morris (Why Vietnam Invaded Cambodia, 1999) argues security and ideology drove the decision; Ben Kiernan (How Pol Pot Came to Power, 1985) acknowledges mixed motives while crediting the anti-genocide effect; this is the orthodox-vs-revisionist tension over Hanoi's intent.
• Judgement. The security reading carries most weight - the timing, the treaty and the decade-long occupation all point to strategic motive - but the humanitarian effect was real, so the view should be defended as "largely, not wholly" true.

MODEL PARAGRAPH (Argument 1)

The timing and triggers of the invasion point firmly to security as Vietnam's driving motive. Democratic Kampuchea had claimed the Mekong Delta as Khmer territory and, from 1977, launched cross-border raids into An Giang, Tay Ninh and Kien Giang, culminating in the Ba Chuc massacre of 18 April 1978, in which around 3,157 Vietnamese civilians were killed. Hanoi's response was not an immediate humanitarian rescue but a calculated strategic build-up: the Treaty of Friendship and Cooperation signed in Moscow on 3 November 1978 secured a Soviet umbrella against Chinese retaliation, and the Kampuchean United Front, formed on 2 December 1978, was assembled to give the coming invasion a Cambodian face. Only then, on 25 December 1978, did Vietnam strike. As Stephen Morris argues in Why Vietnam Invaded Cambodia (1999), the decision flowed from security and ideology rather than concern for Cambodian victims; the regime had, after all, tolerated the worst of the genocide in 1975 to 1977 without acting, moving only when its own border and great-power position were at stake.

Marker's note. A band-6 response keeps "security rather than humanitarian" in view throughout, weighing the two motives rather than describing the invasion, anchors each claim in dated evidence (Ba Chuc 18 April 1978, treaty 3 November 1978, invasion 25 December 1978), and sets Morris against Kiernan in genuine tension. Accepting Hanoi's later humanitarian justification at face value, or simply narrating events, caps the response in the middle bands.