When an ally of the Ü-Tsang ruler threatened destruction of the Gelugpas again, the fifth Dalai Lama Lozang Gyatso pleaded for help from the Mongol prince Güshi Khan (1582–1655), leader of the Khoshut (Qoshot) tribe of the Oirat Mongols, who was then on a pilgrimage to Lhasa. Güshi Khan accepted his role as protector, and from 1637–1640 he not only defeated the Gelugpas' enemies in the Amdo and Kham regions, but also resettled his entire tribe into Amdo. Sonam Chöpel urged Güshi Khan to assault the Ü-Tsang king's homebase of Shigatse, which Güshi Khan agreed upon, enlisting the aid of Gelug monks and supporters. In 1642, after a year's siege of Shigatse, the Ü-Tsang forces surrendered. Güshi Khan then captured and summarily executed Karma Tenkyong, the ruler of Ü-Tsang, King of Tibet.

Who did the 5th Dalai Lama beg for help from?