"No god but God"

During my vacation I read "No god but God," by Reza Aslan, an Iranian-American scholar of Islam.. This is a very detailed account in a secular format of the history of Mohammed and his teachings, the development of the Koran and the schisms that beset the movement of Islam from the beginning.
Certain topics stand out for me. For example, according to Aslan, Mohammed's main motivations for preaching against the rulers of Mecca, the Quraysh tribe, was that they cruelly exploited their economic dominance over other tribes in Mecca, and that they allowed idols to be housed inside the Kaba, the great black stone cube that was and still is the center of Arab veneration. Because Mohammed's quarrels with the Quraysh became so heated he was forced to leave Mecca for Medina, then called Yathrib, and this is counted as the beginning of Islam in 622 ce. It was there that he set up his model community and forged his new religion. When he returned to Mecca with an army in 630 ce it capitulated to his forces, and he captured the Kaba and destroyed the idols, but he did not destroy the Kaba itself. It is still a focal point for all pilgrimages (hajj) to Mecca.
It is acknowledged that Mohammed approved the murder of the Jewish clan of Qurayza in Medina (not to be confused with the Quraysh of Mecca). This is taken as evidence of Mohammed's anti-Jewish proclivities. But, Aslan argues a more balanced vewpoint. Specifically: 1. The "Jewish tribes" of Yathrib/Medina were converts to Judaism, they were not originally Jews but Arabs, and their adherance to Judaism was superficial; 2. Mohammed had personally pardoned two other Jewish clans who refused to join his band, and had allowed them to leave Yathrib with all their belongings to settle elsewhere; 3. Mohammed gave in to the entreaties of his followers in accepting the killing of the Qurayza (600 men and boys) rather than making the decision himself, and in doing so they were treated as they treated other Arab clans who fought them and lost.
The schism over the succession to Mohammed resulted partly because Mohammed gave no indication of his preference when he died in 632 ce. When his grandson Ali was passed over, this lead to the split of the Shia from the Caliphate of the Sunnis, a division that was finalized at the battle of Karbala in 680 ce when the natural heirs to Ali were murdered. By then there had been four Caliphs and their power had expanded out of all proportion to the beginnings of Islam in Mecca. This is much like the power of Byzantium and Rome that had little connection to the origins of the humble Jewish carpenter's son from Bethlehem. These wars of succession and doctrinal splits are symptomatic of all successful/powerful religions.