In the 15th century, Mongolia was split into two groups called the Oirad and the Khalkha and for a short period the Oirad, under the rule of Dayan Khan, reunited Mongolia. In the 16th century, the Mongols came to rule a considerable part of Asia and even defeated the Khalkhas. After his death, Mongolia once again split into waring groups but was again brought together by Altan Khan. Under his rule, they continued to invade China but in 1571 they signed a treaty with the Chinese Ming Dynasty. Next he invaded Tibet, converted to Buddhism and named the first Dalai Lama.