China has, in the last few years, demanded that India turn over a contested area in northeast India (Arunachal Pradesh, which China claims as a part of Tibet). China then escalated its demands by refusing to allow Indians born in the disputed area to visit China. This Chinese behavior has angered India, which two years ago implemented a five year plan to increase their ability to deal with any Chinese aggression against Arunachal Pradesh. The Chinese claims have been on the books for decades but in the last four years China has become more vocal about it. That's one reason India has been rapidly increasing its defense spending. But since both nations have nuclear weapons, a major war over Arunachal Pradesh is unlikely, but not impossible.
India fears that China might try to carry out a lightning campaign (a few days, or a week), and then offer peace terms (with China keeping all or part of Arunachal Pradesh). Since neither country would be willing to start a full scale nuclear war over Arunachal Pradesh (a rural area with a population of about a million people, spread among 84,000 square kilometers of mountains and valleys), the "grab and parley" strategy has to be taken seriously. In the meantime, China keeps finding ways to annoy India over this issue.
Meanwhile, India seems quite confident that they can handle China if a war breaks out in this mountainous wilderness. Partly that's because India is playing defense here, which always confers an advantage. But India's big advantage is that it has recent (1999) combat experience in mountain warfare. China has not fought since 1979, and what was in the hill country on the Vietnamese border. Not only was India's combat experience recent but it was in the same mountain range (the Himalayas) where they face China.
That 1999 war got little publicity, so it's generally unknown outside India how much that experience changed the Indian armed forces. That's not surprising. The foe in that war, Pakistan, did not even officially admit to its role in that undeclared war until 2010. Pakistan had always insisted that India was just fighting Islamic terrorists (who were just trying to liberate Kashmir from Indian rule) in 1999. But two years ago the names of 453 soldiers killed in "the Kargil war" were posted on the Pakistani Army website. Although the Pakistani troops, masquerading as Islamic terrorists, were forced to retreat during the 1999 conflict, Pakistan still considered it a victory (because it garnered much publicity for their terrorism campaign in Kashmir and India chose not to mount a major invasion of Pakistan). India lost about 550 troops in the fighting. The elected Pakistani government of the time was opposed to the Kargil operation and tried to remove the head of the armed forces (general Pervez Musharraf). In response, Musharraf staged a coup and ruled the country for the next nine years.
Although the Indians succeeded in forcing the Pakistanis to retreat, the unexpected conflict exposed deficiencies in the equipment, training, and tactics of the Army and Air Force, as well as the ability of the two services to coordinate their operations. The Indian military was not keen on giving a lot of publicity to the problems they had during the 74 day Kargil campaign. But in the last decade it's been noted that Indian military reformers often invoke Kargil, and that tends to help overwhelm opposition to needed changes. This has led to more attention being paid to what went on during the high altitude (4,000 meters and up) conflict.
As a result of Kargil the army has purchased a lot of new high-tech gear for its infantry, revised training methods, and even changed the organization of infantry battalions. The air force has bought more heavy transports (American C-17s) and set up closer and continuous coordination with the army and navy. The air force has studied the unique conditions encountered over these high mountains and trained their pilots to deal with it. The Chinese are just now catching up with this item.
Initially, the impetus behind all these reforms was to avoid another "messy victory" as had been achieved in 1999. But nine years later China started making territorial demands about similar high mountain terrain to the east of Kargil. While initially scary, as the Indians reviewed their readiness for such a conflict they realized they were still in the midst of reforms intended to improve their mountain warfare capabilities. Now it was China's turn to wonder if they were ready for war in the Himalayas.