In the 9th century, Buddhist tradition records a contested succession, but there are many inconsistencies; contemporary Chinese histories indicate that Tibetan unity and strength were destroyed by rivalry between generals commanding the frontier armies. Early in the 9th century a scion of the old royal family migrated to western Tibet and founded successor kingdoms there, and by 889 Tibet was a mere congeries of separate lordships.

Tibetan generals and chieftains on the eastern border established themselves in separate territories. The acknowledged successors of the religious kings prospered in their migration to the west and maintained contact with Indian Buddhist universities through Tibetan scholars, notably the famous translator Rin-chen bzang-po (died 1055). In central Tibet, Buddhism suffered an eclipse. A missionary journey by the renowned Indian pandit Atisha in 1042 rekindled the faith through central Tibet, and from then onward Buddhism increasingly spread its influence over every aspect of Tibetan life.

Inspired by Atisha and by other pandits whom they visited in India, Tibetan religious men formed small communities and expounded different aspects of doctrine. Atisha's own teaching became the basis of the austere Bka'-gdams-pa sect. The Tibetan scholar Dkon-mchog rgyal-po established the monastery of Sa-skya (1073), and a series of lamas (Tibetan priests) founded several monasteries of what is generally called the Bka'-brgyud-pa sect.

Hermits such as Mi-la ras-pa (1040-1123) shunned material things; but the systematized sects became prosperous through the support of local lords, often kinsmen of the founding lama, and, except for the Bka'-gdams-pa, each developed its own system of keeping the hierarchical succession within a noble family. In some sects the principle of succession through reincarnation was evolved. Although lamas of different schools studied amicably together, their supporters inevitably indulged in worldly competition. This tendency was intensified by the intervention of a new Asian power, the Mongols.