What if Rashidun Caliphate survived? What if Muawiya never fought with Ali, what if the Shia movement was never born? Islamic Caliphate conquer almost all of Old World, and Islam is main influence in world, not Western. In 656 A.D, Ali ibn Abi Talib Grant insistence that Uthman's killers sentenced to death. Finally, the rebellion died down after Ali started fighting against the Kharijites, the perpetrators of the murder of Uthman ibn Affan.
First Wave to Byzantium
Caliph Ali sent an envoy to Emperor of Byzantium, to discuss boundary treaties. But, Byzantine Emperor ordered his soldiers to behead and impale the envoy, as a sign that he will not negotiate with Rashidun Caliphate. Caliph Ali declare war to Byzantine Empire, and start Muslims first wave to Byzantium.
In 659 AD, the fleet of Muslim warships start sailed to Cyprus. Meanwhile, the Caliphate Troopers start attack Cappadocia. They attack was success. In Sicily, Islamic Emirate attacked the Italy States. But unfortunately they failed, and the Crusaders conquer Emirate of Sicily.
In 661, Caliphate had reach Constantinople, blockading it. But, in one year, they never entered the city, because Constantinople is have supply from Macedonia, and strait between Turkey and Constantinople is blocked by giant fortress, and Byzantium have the Greek Fire. Caliph hold a big contest, who can create weapon to defeat the Constantinople, he will be given a great gift, 20 thousands dinars.
In 662, Abu Ammar Al Farsi, scientist and alchemist from Persia created "Arab Fire". This weapon is used by Caliphate Army to attack Constantinople. After one year, Constantinople fall. Emperor is killed, and General Fergus is sign the Treaty of Damascus. Byzantium conquered, and Caliphate become the large empire.