In 1615, when the Oirats were still under the suzerainty of the
Khalkha leader
Ubasi Khong Tayiji, the elite had largely converted to Tibetan Buddhism. However, the period saw a rise in internal religious rivalries within Tibet, in particular between the
Gelug and
Karma Kagyu schools. The main Gelug religious figure church was the
Dalai Lama while the Karma Kagyu was supported by the dynasty of the
Tsangpa based in Samdrubtse (modern
Shigatse). They, in turn, found support from groups of Khalkhas and
Chahars.
Sonam Rapten was the chief attendant during the youth of the
5th Dalai Lama (1617–1682). He drew up plans to end the persecution of the Gelug and unify Tibet with the help of Güshi. The Gelug monasteries appealed for help against the
Karmapa and
Bon partisans such as the Khalkha prince
Choghtu Khong Tayiji, who had recently settled in
Amdo. This was a very bold move since the Mongols had a reputation for ruthlessness against military foes and civilians alike. Güshi was known for his devotion to the Gelugpa and responded positively. He was joined in a pro-Gelugpa league by the other Oirat princes: his nephews Uchirtu Sechen and Ablai Tayiji in the
Zaysan and
Ertis areas; furthermore
Erdeni Batur, whose
Dzungar and
Dörbet Oirat subjects lived by the
Ulungur,
Irtysh and
Emil Rivers, and even the
Torghut chief
Kho Orluk, who was in the process of subduing areas to the north of the
Aral and
Caspian Seas. As it turned out, it would nevertheless take several years to install the "Great Fifth" as the head of a unified Tibetan state. In the company of the Dzungar prince Erdeni Batur, Güshi marched into
Qinghai with 10,000 Oirat troops in 1636. In the next year, he confronted the Khalkha forces of Choghtu Khung Tayiji, which were 30,000 strong and were opposed to the Gelugpa sect. A battle took place in 1637, on the Kokonor Gorge and is known as the
Battle of the Bloody Hill. The Choghtu troops were defeated and scattered, and the survivors had to surrender. Choghtu himself hid in a marmot hole but was found and killed on the spot. In that way the Khalkhas were suppressed in Tibet a short time after they were subjugated in
Mongolia by the invading
Manchu people. Güshi proceeded to
Ü-Tsang in 1638 as a pilgrim. There he received religious instructions from the 5th Dalai Lama. During a ceremony in
Lhasa, he was placed on a throne and proclaimed "Holder of the Doctrine
Chogyal" (, ). By this time he was also known by the title of
khagan, adopted in defiance of the
Borjigid (the
direct descendants of Genghis Khan). Güshi invited the Dalai Lama to visit his territories, but the Great Fifth was unable to do so due to the unstable circumstances in Ü-Tsang. He did, however, send a permanent representative to the Khoshut to maintain good relations. Güshi Khan returned to his newly conquered realm in Qinghai, where the Khoshuts resolved to settle down. ==Invasion in Kham==