One faction was a group of ‘Alids who believed that ‘Ali should inherit the mantle of Islam and referred to traditions suggesting that Muhammad had proclaimed to the faithful that ‘Ali should be his successor. The amsar followed the ‘Alids and later adopted the Shi‘a appellation. The other faction, the Umayyads contended that the method of appointing successors should be by consensus, as was done with the first caliphs. Mostly based in Mecca, they later identified as Sunnis. Over time, these factional differences became increasingly difficult to bridge.

Arabs employed more aggressive tactics, making use of their mobile light cavalry against their enemies’ heavily armored armies. Once victorious, the Arabs populated garrison cities on the frontier, called amsar, with Muslims.

Byzantine and Persian empires had been severely weakened from near-continuous fighting, dating back decades prior to the rise of Islam, so they both suffered from the fatigue of war

Antioch, Aleppo, and Jerusalem fell to the Muslims not long thereafter. ‘Umar appointed Mu‘awiya, a member of the Meccan Umayyad aristocracy to govern Syria at his behest.

The majlis chose ‘Umar (634 – 644), a close friend of Abu Bakr, to be the next caliph. ‘Umar had been the military power behind Abu Bakr. A dynamic and uncompromising leader, ‘Umar recognized the necessity of expansion northward to achieve various ends. First, he sought to subdue the security threat of raiding nomads, many of which remained a law unto themselves. Second, in his struggle to contain discontent, he used the cohesive element of jihad to unite the Muslim community against unbelievers and expand God’s dominion.