本文重新考訂僕固氏世系，指出以往研究認為的唐代僕固氏第五代設支是誤植阿史德覓覓事跡，而曳勒歌與乙李啜拔為同一人名的不同音譯，為僕固懷恩之父。本文又考證出阿跌部與突厥汗室阿史那部及舍利部均存在姻親。開元初年內附唐朝的鐵勒諸部不久返回漠北，其中部分受到突厥汗庭打擊。經此變動，阿跌部在登利可汗統治時期進入後東突厥汗國政治核心集團，而僕固部則在被毗伽可汗出征失敗後持騎牆態度，與突厥汗室不睦而與迴紇關係曖昧。唐廷對僕固懷恩的信任可能淵源於他與迴紇的特殊關係，而當肅、代之際唐紇關係趨於緊張之後，懷恩在內附蕃部中變得孤立無援。碑誌材料可證明僕固懷恩曾於廣德元年叛亂之後進攻承天軍，證實他與作為安史舊部降唐的河北藩鎮之間確實存在暗通，可能損害與其本無淵源的河東實權派將領利益。僕固懷恩的種種越位之舉加速了原本對其持保留態度的內附蕃部與其河東實權派的合作，導致僕固懷恩叛亂的失敗。

Alpqapa, Pugu Huai'en's father, led his tribe to the Tang court in the early Kaiyuan period, but after a short while came back to the Turkic court, and took sides with both the Turkic court and the Uighur tribes. At the same time, Ädiz kept marriage relationships with both the Turkic court and Sharï. Since Pugu kept a close relationship with the Uighurs, they became isolated from the tribes that surrendered. The trust between the Tang court and Pugu Huai'en was based on his special relationship with the Uighur Empire, so when the Uighurs became hostile toward the Tang, Pugu Huai'en became isolated and dangerous. Considerable evidence shows that Pugu Huai'en assaulted Chengtianjun after his rebellion, which means he wanted to get touch with Hebei warlords, that is leaders who had surrendered after the An Lushan Rebellion. This threatened the Hedong warlords, who then built an alliance with foreign tribes against Pugu Huai'en and forced him to leave Hedong.