The Vietnamese weren't going to expand into South East Asia; they intervened in Cambodia to topple the Khmer Rouge, who initiated hostilities by attacking Vietnamese border towns. Indonesia had already crushed the communist insurgencies; the Philippines had crushed the communist Huks in the mid 1960s.
Your country called Japan also supported, so you need to shut up or learn history, my friend.
Response from the international community
Shortly after the fall of Phnom Penh to Vietnamese forces and their Kampuchean allies in January 1979, representatives of Democratic Kampuchea called for an emergency meeting of the
United Nations Security Council, so Prince
Norodom Sihanouk could present the deposed regime's case. Despite strong objections from the Soviet Union and
Czechoslovakia, the UN Security Council gave Sihanouk this chance.
[43] Although Sihanouk distanced himself from the human rights abuses of the Khmer Rouge, he accused Vietnam of using aggression to violate Kampuchea’s sovereignty. As such, he demanded all UN countries to suspend aid to Vietnam and not recognise the Vietnamese-installed regime.
[43] Subsequently, seven non-aligned members of the UN Security Council submitted a draft resolution calling for a ceasefire and the withdrawal of all foreign forces from Kampuchea, which was endorsed by China, France, Norway, Portugal, the United States and the United Kingdom. However, the resolution was not approved due to strong opposition from the Soviet Union and Czechoslovakia.
[42] Critics of Vietnamese actions held that they did not invade Cambodia out of any noble desire to stop the atrocities committed by Pol Pot's regime but rather to consolidate their domination of Indochina.
[44]
Between 16–19 February 1979 Vietnam and the new Kampuchean regime held a summit meeting which concluded with the two countries signing the Treaty of Peace, Friendship and Cooperation.
[45] Article 2 of the treaty stated that the security of Vietnam and Kampuchea were interrelated; thus they would help defend each other “against schemes and acts of sabotage by the imperialist and international reactionary forces”, thereby legitimising the presence of Vietnamese troops on Kampuchean soil.
[43] Soon afterwards, the Soviet Union, the socialist countries of Eastern Europe and India immediately recognised the Vietnamese-installed People’s Republic of Kampuchea. The Soviet Government praised the PRK's "remarkable victory" and expressed its full support for the regime's advance towards socialism. Furthermore, the Soviets harshly criticised the Khmer Rouge regime's record of terror, which they implied had been imposed by China.
[43]
At the 34th Session of the
UN General Assembly, representatives of the People's Republic of Kampuchea and Democratic Kampuchea both claimed the right to represent their country. The former also notified the member nations of the UN Security Council that it was the sole legitimate representative of Kampuchea and its people.
[45] In response, the UN Credentials Committee decided to recognise Democratic Kampuchea by a vote of six to three, despite the Khmer Rouge's blood-stained record while in power. Accordingly, representatives of Democratic Kampuchea were allowed to be seated in the General Assembly, with strong support from China.
[46] By January 1980, 29 countries had established diplomatic relations with the People Republic of Kampuchea, yet nearly 80 countries still recognised the legitimacy of the deposed Democratic Kampuchea. At the same time, the Western powers and the member countries of the
Association of South East Asian Nations (ASEAN) also voiced strong condemnation of Vietnam’s use of force to remove the Khmer Rouge regime.
[43]
Thailand, which shares an 800-kilometer (500-mile) border with Kampuchea and has historically feared Vietnam's expansionism, demanded that Vietnam immediately remove its troops from Kampuchea so its people could elect a government free from foreign intervention.
Indonesia,
Malaysia, the
Philippines and
Singapore showed their support for Thailand's position.
[43] Furthermore, ASEAN viewed Vietnam’s invasion and subsequent occupation of Kampuchea, which received strong Soviet support, as an intolerable threat to the region’s security and stability.
[47] That view was shared by China, which went as far as accusing Vietnam of forcing Kampuchea into an Indochinese federation to serve as an outpost of Soviet global hegemony. The United States, which never maintained any form of diplomatic ties with the Khmer Rouge’s Democratic Kampuchea, showed strong support for the membership of their former enemy in the UN General Assembly, and echoed ASEAN's call for an immediate withdrawal of Vietnamese military forces from Kampuchea.
[43]