Face-off at 14,000ft China and India have been to war over their Himalayan border before. Is it about to happen again?

China and India are the closest they’ve been to armed conflict in half a century, over a mountainous strip of land on their disputed border high in the Himalayas.

On June 15, at least 20 Indian soldiers were killed in a violent brawl between the two sides in the disputed region of Aksai Chin-Ladakh. Soldiers fought with fists, stones, and nail-studded bamboo poles, according to a source in the Indian military.

It is unclear if any Chinese soldiers died, but both governments have moved fast to find a diplomatic solution to the worst outbreak of border violence in decades.

In 1962, India and China went to war over this remote, inhospitable stretch of land. Thousands died, though there are conflicting figures on the final toll.

Since then, the two countries have had a long history of non-lethal scuffles over the position of the border.

The problem is that neither side agrees where it is, how far it stretches, nor who owns the surrounding territory.

There are three main areas of contention along India and China’s disputed border, broadly known as the Line of Actual Control.

That name dates back to 1959 when former Chinese Premier Zhou Enlai proposed that troops on both sides withdraw behind a “line up to which each side exercises actual control.”

The western section, where the most recent clash took place, divides India’s Ladakh region and the Chinese-administered Aksai Chin in the heavily-contested Kashmir region.

The central section runs along the northern borders of the Indian states of Himachal Pradesh and Uttarakhand and southern Tibet.

The eastern section runs between southern Tibet and far eastern India, following the McMahon Line, named after the British colonial administrator who proposed it in 1914. It was in this region that the last major standoff between India and China took place in 2017.

The border between Ladakh and Aksai Chin is a result of the 1962 war between India and China, roughly marking where the two armies finished fighting more than half a century ago.

Although the LAC appears as a clear line on a map, no one knows exactly where it falls. That’s due to due to a combination of historic disagreements, clashing territorial claims and poorly-defined maps.

It means that on the ground, Chinese and Indian soldiers regularly come into conflict with each other, claiming certain parts of the territory as their own.

The confusion over the LAC in Aksai Chin dates back to at least 1947 when India and Pakistan went to war, resulting in the partition of the region.

After that conflict, the border between the countries was far from settled. India, China and Pakistan all claimed parts of the northern region of Kashmir.

In subsequent years, tensions between China and India grew. New Delhi was infuriated when Chinese troops built a road through Aksai Chin in 1957, while Beijing was displeased at the Dalai Lama’s flight to India after the Tibetan uprising in 1959.

In 1962, the two countries went to war over Aksai Chin. But the Chinese forces were better supplied and, as many came from the plateaus of Tibet, were more acclimatized to the high altitude of the Himalayan battlefields, according to an essay published on the war in 2003.

China pushed back Indian troops and took possession of the region. At least 2,000 troops were killed, with twice as many Indian fatalities as Chinese.

Before the war, Chinese leader Mao Zedong said the 1962 conflict would keep the border between the two countries stable for 10 years, but it barely lasted five.

Tensions flared again in 1967 along two mountain passes, Nathu La and Cho La, in the Indian state of Sikkim. That time, India pushed the Chinese back. Reports at the time said that 150 Indians and more than 300 Chinese were killed in the ensuing conflict.

Relations between the two countries have improved since — the last fatal encounter before this year was in 1975 — but with neither side agreeing on a border and New Delhi continuing to claim Aksai Chin, the mountainous area remains volatile.

India and China agreed in 1993 to ensure that the border was peacefully maintained but no serious efforts have been made to define it. And soldiers have often clashed in non-military ways i.e. in brawls and using makeshift weapons.

Border tensions aren't limited to Aksai Chin and the Kashmir region.

The last major standoff between China and India took place in Doklam in 2017, in the eastern section of the LAC, at their border with Bhutan in the Himalayas.

Bhutan accused Chinese troops of building a road inside its territory, a claim its ally India supported.

Troops massed on both sides of the border and China staged live fire drills to intimidate its neighbor.

Eventually talks calmed the situation and soldiers were withdrawn.

The border situation is further inflamed by fractious geopolitical relationships in the region.

In particular, China’s close relationship with Pakistan complicates Beijing’s relations with India, Islamabad’s longtime rival in South Asia.

Experts say decades may have passed but the two sides are no closer to mutually defining their borders.

“I think an agreement will take time and need concerted negotiation that should not be sporadic but sustained,” said former Indian Foreign Secretary Nirupama Rao.

Publicly, China and India are downplaying border tensions and say they are holding emergency meetings to try to defuse the situation.

Chinese Foreign Minister Wang Yi told his Indian counterpart in a phone call Wednesday that both sides should “properly address the border situation through existing channels” so that they can “jointly preserve peace and tranquility in the border area.”

But it could turn in an instant.

“I believe that the next few weeks are going to be reasonably tense,” said retired Lt. Gen. Syed Ata Hasnain, who previously commanded Indian forces based in Jammu and Kashmir.

“There is no certainty that this is the last of the engagements of this campaigning season between the Indian and Chinese armies.”