This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The Mongol leader Altan Khan met Sonam Gyatso, head of the Gelug school of Tibetan Buddhism, at a summit in 1578. The meeting was an exchange of legitimacy on both sides: Altan Khan received religious sanction for his own rule, and in return bestowed on Sonam Gyatso the title Dalai Lama, a title Sonam Gyatso's own successors, recognised through the tradition's practice of identifying reincarnate teachers, have carried ever since.
The Gelug school gained more from the summit than a title's origin. It gained a powerful patron and, this time, a mandate to convert the wider Mongol population rather than the court alone, the limit that had held back the Sakya school's earlier arrangement with Kublai Khan three centuries before. Gelug Buddhism spread rapidly across Mongolia in the decades that followed, reaching ordinary Mongols rather than remaining confined to elite patronage, and became the dominant faith of the Mongol lands within a relatively short span of those decades.
What this changed for Buddhism's spread was the completion of a process the first, court level introduction under the Sakya school had left unfinished: from 1578 Buddhism became Mongolia's dominant religion in fact as well as at court, a position it held for more than three centuries until the Stalinist purges of the 1930s brought it to a violent and, for a time, near total end.