may have involved violence. However, after six months the group made peace with Abu Bakr and Ali offered him his allegiance. Reign After assuming the office of Caliph, Abu Bakr's first address was as follows: Abu Bakr's reign lasted for 27 months, during which he crushed the rebellion of the Arab tribes throughout the Arabian Peninsula in the successful Ridda Wars. In the last months of his rule, he sent Khalid ibn al-Walid on conquests against the Sassanid Empire in Mesopotamia and against the Byzantine Empire in Syria. This would set in motion a historical trajectory (continued later on by Umar and Uthman ibn Affan) that in just a few short decades would lead to one of the largest empires in history. He had little time to pay attention to the administration of state, though state affairs remained stable during his Caliphate. On the advice of Umar and Abu Ubaidah ibn al-Jarrah, he agreed to draw a salary from the state treasury and discontinue his cloth trade. Ridda wars Troubles emerged soon after Abu Bakr's succession, with several Arab tribes launching revolts, threatening the unity and stability of the new community and state. These insurgencies and the caliphate's responses to them are collectively referred to as the Ridda wars ("Wars of Apostasy"). The opposition movements came in two forms. One type challenged the political power of the nascent caliphate as well as the religious authority of Islam with the acclamation of rival ideologies, headed by political leaders who claimed the mantle of prophethood in the manner that Muhammad had done. These rebellions include: that of the Banu Asad ibn Khuzaymah headed by Tulayha ibn Khuwaylid that of the Banu Hanifa headed by Musaylimah those from among the Banu Taghlib and the Bani Tamim headed by Sajah that of the Al-Ansi headed by Al-Aswad Al-Ansi These leaders are all denounced in Islamic histories as "false prophets". The second form of opposition movement was more strictly political in character. Some of the revolts of this type took the form of tax rebellions in Najd among tribes such as the Banu Fazara and Banu Tamim. Other dissenters, while initially allied to the Muslims, used Muhammad's death as an opportunity to attempt to restrict the growth of the new Islamic state. They include some of the Rabīʿa in Bahrayn, the Azd in Oman, as well as among the Kindah and Khawlan in Yemen. Abu