Why did tribal rivalries weaken the later Umayyad caliphate?

Tribal rivalries significantly weakened the later Umayyad dynasty by undermining the military and political cohesion of the caliphate.12

The Umayyad state was organized along Arab tribal lines, and the resurgence of long-standing feuds between northern (Qays) and southern (Kalb) Arab tribes severely reduced the regime's military effectiveness. These internal conflicts erupted into major revolts across key regions, including Syria, Iraq, and Khorasan, during the mid-8th century.1

These divisions were exacerbated by broader social and political discontents, such as the resentment of non-Arab converts (mawālī) toward the Arab-dominated social structure and the perception among many Muslims that the Umayyads were overly secular and worldly. This instability left the dynasty vulnerable to the Abbasid revolution, which ultimately overthrew the Umayyads in 750 following their defeat at the Battle of the Great Zab River.134