The Mongols invaded Tibet in 1240 with a small campaign led by the Mongol general Doorda Darkhan[33][34] that consisted of 30,000 troops,[35][36] suffering 500 casualties.[37] The Mongols withdrew their soldiers from Tibet in 1241, as all the Mongol princes were recalled back to Mongolia in preparation for the appointment of a successor to Ögedei Khan.[38] They returned to the region in 1244, when Köten delivered an ultimatum, summoning the abbot of Sakya (Kun-dga' rGyal-mtshan) to be his personal chaplain, on pains of a larger invasion were he to refuse.[39] Sakya Paṇḍita took almost 3 years to obey the summons and arrive in Kokonor in 1246, and met Prince Köten in Lanzhou the following year.