SINGAPORE — Prime Minister Lee Hsien Loong’s Facebook post on Vietnam’s invasion of Cambodia in the 1970s has triggered strong overseas reactions, with Cambodian Prime Minister Hun Sen expressing “regret” over Mr Lee’s post.

Mr Lee’s post last Friday (May 31) was intended to express his condolences on the death of former Thai premier, General Prem Tinsulanonda, on May 26.

Mr Lee had said the former Thai leader's premiership coincided with the then-five Association of South-east Asian Nations (Asean) members — Indonesia, Malaysia, the Philippines, Singapore and Thailand — coming together to oppose "Vietnam's invasion of Cambodia and the Cambodian government that replaced the Khmer Rouge".

Aside from his Facebook post, Mr Lee also said in his keynote speech later that Friday at the Shangri-La Dialogue that Vietnam’s invasion of Cambodia posed a serious threat to its non-communist neighbours, while he recounted the formation of the regional grouping of Asean.

It sparked a flurry of reactions from Cambodian Defence Minister Tea Banh and Vietnam’s Foreign Affairs Ministry, as they expressed disagreement over Mr Lee’s comments.

In response to media queries on Friday (June 7), Singapore’s Foreign Affairs Ministry said, among other things, that Singapore “highly values” its relations with Cambodia and Vietnam. Mr Lee’s references to the Vietnamese invasion of Cambodia are “not new” and reflect Singapore’s long-standing viewpoint, the ministry added. 

For those unfamiliar with the Vietnamese occupation of Cambodia, the following are the key developments you need to know.

WHAT WAS THE INVASION AND OCCUPATION ABOUT?

At the time of the invasion, there was already a proxy fight between China and the then-Soviet Union. Although China was previously an ally to the Soviet bloc, it had become openly opposed to the Soviet Union since the early 1960s.

Cambodia was aligned with China, while Vietnam was close to the Soviet Union.

In the early 1970s, Cambodia-Vietnam relations were tense, with the leadership in both countries eyeing each other suspiciously.

Why? Because Cambodia felt that Vietnam still wants to create an IndoChinese federation and install itself as the leader, historians have said.

Three years before the invasion, small clashes between Vietnam and Cambodia had already broken out. But in December 1978, Vietnam launched a full-scale invasion.

Vietnam said that it invaded Cambodia to liberate its neighbour from the despotic Khmer Rouge regime led by Pol Pot, which had committed a genocide of more than 1.7 million people between 1975 and 1979.

However, some historians have put forth a contrarian argument. They pointed out that Vietnam’s invasion and occupation were done out of “self-preservation”. It wanted to oust an anti-Vietnamese government in Cambodia and put in place a puppet government that would support Vietnamese interests.

Aside from the Sino-Soviet proxy, the Cambodia-Vietnam war — which only ended in 1991 — also took place against the backdrop of the Cold War between the two superpowers at the time: The United States and Soviet Union. It was a time when countries were divided into the communist and non-communist blocs.

A communist Vietnam, which had invaded and occupied Cambodia, rattled its surrounding neighbours in South-east Asia, some of which were staving off communism in their own countries, historians said. And there was a need to contain Vietnam’s communist influence.

WHAT IS SINGAPORE’S POSITION ON THE OCCUPATION?

Back in November 2011, former Deputy Prime Minister Wong Kan Seng outlined Singapore’s position on the Vietnamese occupation of Cambodia.

It was an issue which Singapore “took a stand and held firm based on our principles'', he said in a speech at the S Rajaratnam Lecture that year.

Singapore and Asean “contested” the Vietnamese occupation of Cambodia, which happened in the 1970s, he said.

Singapore's involvement in the Vietnam-Cambodia war was not about its ties with Vietnam, as it had “no wish to interfere in the affairs of others or tell them how they should order their house”.

In his meeting with Vietnamese leaders then, Mr Wong — who was foreign minister from 1988 to early 1994 — told them: “We had no sympathies for the Khmer Rouge regime. It was an issue of principle.”

He said: “We made clear that once the issue was settled, we would be ready and willing to render whatever assistance we could to Vietnam... We did not agree with their actions in Cambodia, but learnt to respect each other as serious countries.”

Mr Wong said that the issue for Singapore was that Vietnam’s invasion was “a clear case of violation of international borders and an act of external aggression, which would have established an undesirable precedent of international relations if left unopposed”.

He added: “We had to respond. Anything less would have undermined our credibility and posed serious implications for our own security.”

A key lesson from the conflict, Mr Wong stressed, was that peace was a “necessary condition for the political and economic survival of small countries like Singapore”.

WHAT DID ASEAN DO ABOUT IT?

Mr Wong noted that leading up to the signing of the Paris Agreement in 1991 — which would end the conflict — Asean had three key objectives to achieve.

They were: To prevent the Vietnamese occupation of Cambodia “from becoming a fait accompli”, bring Vietnam to the negotiating table and ensure a peaceful settlement that allowed Cambodian people the right to self-determination and independence.

“We did not seek a restoration of the status quo ante which would have seen a return of the Khmer Rouge. That was unacceptable,” he added.

“On this point of principle, we clashed with China and even with the US that initially sided with China against us and Asean.”

A month after the conflict broke out, the Asean foreign ministers convened a special meeting in Thailand’s capital of Bangkok in January 1979, Mr Wong said.

He added that the ministers put out a statement strongly condemning Vietnam for violating Cambodia’s independence, sovereignty and territorial integrity.

The regional grouping also campaigned vigorously on the issue at the UN, focusing on denying Vietnam the opportunity to claim Cambodia’s seat at the UN General Assembly.

“With intense lobbying, we pushed through the Asean resolution in support of Cambodia year after year with increased majorities,” Mr Wong said. “Our goal was to keep the issue in international consciousness and persuade Vietnam to come to the negotiating table.”