King Sindeok(神德王), King Kyeongmyeong(景明玉), and King Kyeongae(景哀王) who were on the throne during 912-927 sprang from the Baks. It is hard to regard the establishment of the Baks' Royal family as the foundation of new dynasty, because King Sindeok ascended the throne by force of Yegyeom(乂兼). The Baks' Royal family failed to make clear the difference from Kyeongmoon's Royal family and to recovery its royal authority. The causes which the Baks' Royal family went to ruin were as follows. The first cause was a fall of its royal authority. The Royal family after Queen Jinseong(眞聖女王) fell from its royal authority, depending on a man of power and lost its traditional authority by the appearance of Goryeo and later Baekje. The second cause was a failure of its foreign policy. Its foreign policy of pro-Goryeo but anti-later Baekje cast the balance of power among three countries and brought about later Baekje's invasion which led to King Kyeongae's death. The third cause was a economic slump of its capital. The unusual changes in the weather which repeated every year under the reign of King Hyogong and King Sindeok were a heavy blow to its economy. The fourth cause was a excessive dependence on religion of the ruling class. They depended excessively on religion to pray to God for protection. King Kyeongae was absorbed in religious ceremonies such as his own worship at a shrine and a large Buddhist lecture meeting(Ef.!t.~ 1r). A excessive dependence on religion of the ruling class obstructed a realistic judgment and management. The main cause of the fall of Silla was the misrule of the Bak's royal family which didn't overcome a national crisis by its own ability but depended on a religion or the protection of Goryeo.