NEW DELHI — First it was cellphone towers, new roads and surveillance cameras, popping up on the Chinese side of the disputed Himalayan border with India.

Then it was more run-ins between troops on each side, pushing, shoving and eventually getting into fistfights.

Then, about three years ago, Indian soldiers spotted their Chinese foes carrying iron bars with little numbers written on them — a weapon apparently issued as standard gear, and a sign that the Chinese were gearing up for hand-to-hand combat.

“This is how China operates,” said J.P. Yadav, a recently retired official with the Indo-Tibetan Border Police, on the Indian side. “These are very planned things.”

Now, weeks after a deadly brawl erupted along the border, thousands of Chinese and Indian troops are amassed over a contentious, jagged line in one of the most remote places on earth. Satellite photos reveal a major Chinese buildup, including a blizzard of new tents, new storage sheds, artillery pieces and even tanks.

Each country has accused the other of provocative actions along the murky border. But according to people who live and work in the region, Ladakh, a Chinese push into Indian territory has been building for years.

The area, high up in the Himalayas, has little obvious strategic value, few resources and few people — it’s difficult to even breathe up there, with much of the terrain above 15,000 feet. But India and China, both in the grip of increasingly nationalistic governments, will not give an inch of territory, even along a border so remote that it has never been conclusively mapped.

The Ladakhis caught in between are a fragile group, numbering perhaps a few hundred thousand. They are Tibetan in culture, identify themselves as Indian and have long been pulled in different directions at the edges of empire.

“If we don’t speak now, it will be too late,” said Rigzin Spalbar, a Ladakhi politician. “The Chinese have intruded and encroached on our land. Even the media is not telling the truth. They are only showing the things that the government wants to them to show.”

Mr. Spalbar and other prominent Ladakhis insist that they have reported Chinese incursions for years, but that the Indian military refused to do anything about it. They say there was a code of silence, in which the Indian media was complicit, and that the Indian armed forces didn’t want to face the fact that a more powerful and aggressive military was steadily nibbling away at its territory.

Indian Army officials declined to comment for this article. Chinese officials have been stingy with details as well, including about whether any Chinese troops were killed in the clash in June. Western intelligence agents, who see the border as one of Asia’s most dangerous flash points, say they think that China lost more than a dozen soldiers in the fight.

In early July, Prime Minister Narendra Modi of India swooped into Ladakh, rallying the troops while wearing a puffy green army jacket and aviator-style shades.

“Friends,” he vowed, “the era of expansionism is over,” implying that India was willing to push back against China.

Years ago, the two countries agreed that their troops should not shoot at each other during border standoffs. But the Chinese seem to be testing the limits. In the June fighting, which left 20 Indians and an unknown number of Chinese dead, Indian commanders say that Chinese troops used iron clubs bristling with spikes.

Many analysts say that China’s actions in Ladakh mirror the more assertive approach China has taken across Asia, especially in the South China Sea, since its leader, Xi Jinping, took over in 2012.

And Mr. Modi’s brand of renewed Indian nationalism may also have provoked the Chinese. The Indians, too, have also been building military roads along the disputed border, known as the Line of Actual Control. And Indian officials recently promised to take back Aksai Chin, a high-altitude plateau that India says is part of Ladakh but that China controls and claims as its own.

Aksai Chin is “a very important strategic place” to the Chinese military, said Yue Gang, a retired colonel in the People’s Liberation Army. If India were to seize it, he said, it “would cut the transportation between Tibet and Xinjiang,” two restive areas that China is constantly concerned about.

In culture, language, history and Buddhism, Ladakh is close to Tibet. But Ladakhi scholars are firm about one thing: They don’t want to be part of China.

“Ladakhis see themselves as Indians,” said Sonam Joldan, a Ladakhi political scientist.

Up until a few years ago, Ladakhi and Tibetan nomads roamed freely, pushing their herds of goats, sheep and yak across the lonely, high-altitude plains. They used to converge along a stretch of the Line of Actual Control and barter.

The Ladakhis carried Indian products like basmati rice; the Tibetans brought Chinese-made goods like plastic Thermoses. The trading sessions ended, Ladakhis say, after Chinese troops occupied the area.

This is hardly the first time Ladakh has been swept up into geopolitics.

In the mid-19th century, the British helped set up the princely state of Jammu and Kashmir, which seems to stretch endlessly across the Himalayas. The British, who controlled the Indian subcontinent, believed that the bigger the buffer zone against the Russian empire, the better.

So they allowed the maharajah of Jammu and Kashmir to also grab neighboring Ladakh, enabling him to corner the lucrative trade in pashmina wool. This part of Asia is known for its cashmere (the word for which is derived from Kashmir), and Ladakh’s longhaired Changthangi goats produce especially fine pashmina.

But even after several treaties were signed, the border between Ladakh and China was never neatly defined. It snakes across high mountains that few people have ever climbed.

“There were different narratives during the British times,” said Siddiq Wahid, a scholar of Central Asian history. “Aksai Chin was a part of a Tibet, and it was not a part of Tibet, it was part of Ladakh and not part of Ladakh.”

Shortly after India gained independence in 1947 and Pakistan was created, war erupted between the two countries over Jammu and Kashmir. The princely state, which had hoped to stay independent, hurriedly agreed to be part of India, and thus Ladakh became Indian.

In 1950, China invaded Tibet and soon built a road linking it to Xinjiang, slicing through Aksai Chin. The area was so desolate that it wasn’t until several years later that India even found out about the road. This triggered a brief war in 1962 that ended in a disastrous loss for India, and China seized all of Aksai Chin, more than 14,000 square miles.

By the mid-1970s, things had cooled down, at least on the China front. A protocol evolved between Indian and Chinese troops, including a ban on firearms during border standoffs and regular meetings to iron out disputes.

Things were still hot with Pakistan, though. The same piece of territory, Jammu and Kashmir, has propelled India into repeated conflicts with both Pakistan and China — two nations which, like India, have nuclear arms today.

Indian soldiers who served along the China border in the 1980s and 1990s remember friendly interactions with the Chinese troops.

“We used to shake hands and they would take photos with us and we would take photos with them,” said Sonam Murup, a retired officer.

Those visits with the Chinese were welcome distractions. Soldiers stationed along the border had to tramp around a frozen moonscape for weeks, with little food or water.

“We’d wash our face once maybe every 15 or 16 days,” Mr. Murup recalled.

But the bonhomie with the Chinese ended years ago. Ladakhis say Chinese troops have blocked herders’ access to Indian territory in areas like Demchok and Pangong Tso, a scenic lake where several brawls have erupted.

Indian officers say they have tried to follow protocols for avoiding confrontation, like unfurling banners that read “This Is Indian Territory” in English and Chinese, but that the Chinese refuse to listen. Indian commanders acknowledge that their soldiers, too, now carry hand weapons, like bamboo sticks and sling shots.

The Chinese have clearly outpaced India in developing the region, Indian commanders concede, which could give them a strategic advantage in a conflict.

“They have better facilities,” said Mr. Yadav, the former border official. He said China had paved a highway running right along the border and that Chinese border troops were resupplied by military vehicles carrying supplemental oxygen.

But Mr. Yadav said the Indians had some advantages. He claimed the Chinese troops were in poorer shape, saying, “They don’t walk much.”

More important, he added: “They have not seen war, while on our side our soldiers have been waging war every day in Kashmir.”

Hari Kumar and Sameer Yasir contributed reporting from New Delhi, Iqbal Kirmani from Leh, India, and Steven Lee Myers from Seoul, South Korea.