The remnants of the Second Turk Qaghanate (682〜744), which was overthrown in southern Mongolia by a rebel alliance made up of Uighurs, Basmils and Qarluqs, are described as 'Bug-chor in the Old Tibetan document, P.t.1283, written after the fall of the Qaghanate. The name 'Bug-chor has been identified with the name Mochuo 黙啜, which is the Chinese rendering for Qapγan Qaγan (691〜716), although the reason why these remnants were called 'Bug-ehor, (i.e., Qapγan Qaγan) has heretofore not been made clear. This article is an attempt to find out why and analyze the inner workings of the Qaghanate. The author begins with the fact that one Ozmis Qaγan, who was killed by the rebels before the fall of the Qaghanate, was called Mochuo in a certain Chinese imperial proclamation and epitaph. That is to say, the followers of Ozmis Qaγan were continually referred to as Mochuo after the fall of the Qaghanate, which is why document P.t.1283 refers to this group in Tibetan as 'Bug-chor. Ozmis Qaγan was the son of Pan-que Tegin 判闕特勤 of the left sad under the reign of Deng-li 登利 Qaγan; and the term 'Bug-chor dates back to that period of the left sad. 'Bug-chor can also be traced further back to Qapγan Qaγan, after whose death Kol Tegin 闕特勤, the son of Qutlur 骨咄禄 (682〜691) staged a coup d'etat, purged the near relatives and the followers of Qapγan Qaγan, and placed his elder brother, Bilga Qaγan (716〜734), on the throne. During Kol Tegin's purges, the Qapγan family took refuge near the Kara Irtis River, which became the territory of Tuo-xi 拓西 Qaγan, Qapγan's son, and a base of resistance against Bilga Qaγan. Although surrendering to Bilga Qaγan in 720, the Qapγan family rebelled against Deng-li Qaγan after the death of Bilga. The Qapγan family called themselves 'Bug-chor as the direct descendants of Qapγan Qaγan. It was Ozmis Qaγan who became the last leader of this group and the Turk Qaghanate. In conclusion, the author shows the existence of serious political opposition between the two ruling factions of the Turk Qaghanate, in that after the death of Qutlur, the throne was usurped Qapγan Qaγan, then after the latter's death power was grabbed by Kol Tegin in a coup d'etat expressing dissatisfaction with the Qapγan Qaγan faction. The Qapγan family then organized itself as 'Bug-nor in opposition to the coup d'etat and launched a campaign of resistance against Bilga and Deng-li Qaγan.