‛Umar II. ibn ‛Abd al ‛Azīz reigned as caliph for little more than three years (717-720). But he was regarded by later Umayyad caliphs and even by the succeeding ‛Abbāsid dynasty as "the model of Islāmic justice and piety," writes Hans Küng in Der Islam (2004). He was even repected by the dissident Shia.
‛Umar II set it as his goal to unite the Arabs and non-Arabs of the empire. As more and more of the subject people converted to Islām and rose to more prominent roles in imperial society, tensions had risen. It was ‛Umar II who as caliph recognized that the old order of Arab rule over the subject peoples was outmoded. "For him," writes Küng, "the important things were the return to the original Islāmic principles and the re-establishment of the inner unity of the umma [Muslim community]." He declined any attmpts at further geographic expansion. Instead, he tried to improve the quality of imperial government and began religious education programs among the Bedouins and the Berbers of north Africa to increase their commitment to Islām.
He appointed non-Arabs as judges and governors. And he instituted a major tax reform that reduced the inequities between those who were Muslims by family tradition and those who were converts. The latter still had to pay more, but there was a reduction of the previous inequity. After the death of ‛Umar II, the Umayyad dynasty continued in power through 14 caliphs in all , the last being Marwān II. Küng says that these last years of the dynasty were characterized by "innumerable intrigues and revolutions, deposings and appointments, murders, executions and the public exhibition of chopped-off heads."
Al-Walīd II (743-744) was a colorful caliph. His enemies accused him of being, among other things, a heretic and a homosexual. Although something of an intellectual and a poet, he was too erratic to be an effective leader. Küng quotes Julius Wellhausen on al-Walīd II: "It was a curse that he had power."
Yazid III (744) was an ascetic who once rode into Damaskus on a donkey like Jesus into Jerusalem. He carried the head of his murdered predecessor, al-Walīd II, around with him for a month. The lasting theoretical contribution of Yazid III was in relatavizing the role of the ruler: "Obedience is due only to God. Obedience to a [man] therefore only in obedience to God, so long as he himself obeys [God]. If he defies God and calls for defiance of God [that is, to the committing of sins], so he deserves to be defied and killed."
After the death of Yazid III from natural causes in the same year he seized the caliphate, the last Umayyad caliphate under Marwān II (744-750) saw the third Muslim civil war, with Berbers and Shia opposing the caliph, while external enemies (like Turks and Byzantium, ) began seizing parts of the easter territories.
Though the ‛Abbāsid dynasty took the caliphate, the Umayyad dynasty continued to rule in al-Andalus for over two and a half centuries.