The 40th anniversary of the Sino-Vietnamese War went unnoticed in China, as no commemorative activities were allowed in the country – not even any Vietnam-related posts on social media. But this was not the case in Vietnam , as state-run media and newspapers published in-depth features and critical commentaries recalling the fierce fight from February 17 to March 16, 1979. An editorial in The Voice of Vietnam, a Communist Party mouthpiece, called the war a “righteous … struggle to defend the motherland” and condemned China’s “brutal and illogical invasion”.

China should not forget this history. The anniversary provides a good chance for reflection, as many young Chinese lost their lives in the war – also in the name of defending their motherland.

Back then Beijing made no secret of its motivation to teach an “ungrateful” former ally a lesson, after Hanoi apparently switched its alliance to the Soviet Union by signing the Treaty of Friendship and Cooperation with China’s chief rival at the time in November 1978.

The Sino-Vietnamese war was also widely thought of as an effort to stop Hanoi’s campaign to oust the China-backed Khmer Rouge regime in Cambodia , which had taken the form of an invasion of Phnom Penh.

If so, the Chinese campaign was somewhere between pointless and a complete failure, as it failed to achieve either goal. Vietnamese troops remained in Cambodia until the late 1980s, while Beijing-backed Pol Pot was ousted and the rebels were forced to retreat to Cambodia’s remote western region. Hanoi went on to forge an even closer alliance with Moscow as a result of China’s invasion. Nevertheless, the war had a lasting impact not only on the two countries’ relationship, but also on China’s relations with China’s neighbours. It reshaped geopolitics in the region, and its legacy endures today.

The short-lived but bloody military conflict took a heavy toll in terms of casualties as well as economic losses for both countries. While Beijing and Hanoi have failed to provide full details, Western estimates count 28,000 dead Chinese soldiers and a further 43,000 wounded, while putting the Vietnamese casualties at 20,000 to 35,000 – many of them civilians because the war was fought exclusively on Vietnamese soil.

The painful chapter completely destroyed the countries’ traditional friendship, nurtured by their communist founding fathers Mao Zedong and Ho Chi Minh and once described by Chairman Mao Zedong “as close as lips and teeth”.

That friendship was built on a shared ideology and forged by China’s support of Vietnam during the decades it spent at war, first with France and then with the United States, for which Beijing provided billions of dollars in aid and sent about 320,000 soldiers to help its ally.

The Sino-Vietnamese war undermined China’s image as a peace-loving nation and raised suspicions about the non-hegemonic diplomacy it had long claimed to have.

any nations were horrified to see 600,000 Chinese troops cross the 600km border into Vietnam’s six northernmost provinces, just to teach a lesson to an “unthankful” former ally.

The skirmish sowed a seed of hatred and cultivated distrust between the two peoples. The Vietnamese see their war against the Chinese as comparable to their battles after the French and American invasions, as they fought to safeguard their national independence.

It also resulted in continued spats along the armed border throughout the 1980s. There was also further conflict in territorial disputes, including a 1988 naval battle over a contested reef in the South China Sea, before the two sides formally ended tensions and restored full diplomatic relations in 1991.

This friction also rekindled memories of a historical enmity dating back millennia. Chinese incursions into what is today Vietnamese territory go back as far as 1BC. For centuries, many of China’s smaller neighbours were subjects to its imperial rule.

The most unwanted legacy of the war is that it helped reshape today’s geopolitics in the region, pushing a former comrade in arms into the embrace of what was once their former common foe – the US.

Without that bloody war, Vietnam and China would be close diplomatic allies and ideological bedfellows, two of the world’s five surviving communist-ruled and self-declared socialist states, which also include North Korea, Laos and Cuba. Hanoi’s diplomatic relations with Washington have arguably never been better. US President Donald Trump ’s choice of Hanoi as the venue of his second summit with North Korean leader Kim Jong-un – Trump’s second visit to Vietnam since taking office two years ago – speaks volumes.

By Cary Huan - the South China Morning Post - March 3, 2019