Please note: All years are in the Muslim calendar. 1 AH = 622 AD
The emperor of the Byzantine Empire, Heraclius, converted to Islam in 6 AH and declared Islam to be the state religion of the Byzantine Empire. Nobility hated this and Heraclius, describing Christianity to be "mindless worship of the half-god Jesus," shunned Christianity and viewed Islam with its "giving to the poor" as good. In a series of reforms similar to Constantine's, Islam became the religion of the Byzantines.
However, not all viewed the change well. Notably, the Pope of Christianity declared Byzantine territory in Italy to be under his direct control. Declaring what was termed the "Papal Empire," it fell under Frankish influence almost immediately. This strengthened the Merovingians a lot. In addition, Byzantine Spain also declared independence. However, much of the Byzantine Empire remained secure. Non-Muslim dhimmis were taxed and gradually, Islam became the dominant religion of the Byzantines. By that point, Muhammed had unified Arabia under Islam. Caliphate expansionism was reduced by the Muslim Byzantines. Persia would spared from the Sword of Islam. However, another event would rock the Caliphate. Muhammed died and this caused a succession crisis in the Caliphate. The Byzantines, already Graecifying Arabia, decided that the rightful caliph was Ali Talib because of his relation, and therefore, claim to becoming caliph. With Heraclius' support, Talib became the caliph of the Talibid Caliphate. In this period, expansion was unneeded but the Talibids still became a world power. The Ummah was prospering. The Christendom was a whole other story.
Main article: Saracen Crusade
The Christendom was in disarray. The loss of so many ethnic groups to the "Saracens" had wreaked havoc on the region as xenophobia heavily increased. To show that the Christendom still strong, the Pope declared a crusade on the Ummah to regain the Levant in 45 AH. After Christian nationalism was increased to the point that children were leading legions against the Muslims, the war looked pro-Christian. At the same time, similar Muslim nationalism rose in the Byzantine Empire and in the Talibid Caliphate. In 57 AH, the crusade ended and was a failure. Islamization of the Slavs was assured and the Muslim world looked at their victory in pride.
The Sassanid Empire was facing Islamic conversions in the West. The emperor declared Islam illegal and declared Zurvanism, or dualist Zoroastrianism to be the religion of Persia. Sassanid wars with the Arabs proved indecisive mainly due to the fact that the Persians had recovered from the devastation caused by the Byzantine-Sassanid Wars. Overall, the empire was quiet for the time being. However, the Ummah was not so quiet.
Main article: Byzantine-Arab War
The caliph of the Talibid Caliphate hated the widespread Greek influence on his empire. To end it, he declared war on the Byzantine Empire in 64 AH. The war was devastating to the Talibids and Mecca and Medina were both sacked by Byzantine forces. A large amount of territory was seceded to the Byzantines post-war, in 82 AH. Saba was given to the Byzantines. The Byzantine Emperor declared himself Caliph after marrying a relative of Muhammed. Greek influence was now coming into the Talibid Caliphate like mad. However, something much worse for the Byzantine was occurring.
Main article: Byzantine-Frankish War
The Franks hated the Byzantines even when they were Christian. The Berber tribes were being Islamized. This was a major threat to the Visigoth Kingdom. The Franks declared war on the Byzantines in 94 AH. This war ultimately failed, but the Berbers were kept from expansion in the Peace of Constantinople in 113. However, strains in the conflict led to the complete collapse of the Visigoths in 114 and the Papal Empire's annexation by the Franks in 119. The Franks were powerful and territory was being annexed in the ruin of the Visigoth Kingdom.
Main article: Tang-Sassanid War
The Tang Dynasty were powerful, and despite the bloody An Shi Rebellion, the Tang Dynasty expanded into Central Asia to the point that its influence was spreading into Sassanid Turan. This led to conflict between the Sassanid and the Tang. This broke into war in 130. Still remembering the devastation of the Byzantine-Sassanid Wars, the Sassanids abandoned Turan to the Chinese in 141.
Persian Influence in India
Buddhist Indian missionaries were converting parts of Persia to Buddhism. However, the Sassanid authority was cracking down on non-Zoroastrians. The Nestorian minority was being forced into hiding in Central Asia, where some Turks were being converted to Nestorianism. These Turks would eventually venture into Anatolia in the eleventh century. However, the Buddhists fled into the land of the Buddha, India. Taking use of the broken nature of India, these Persians led by Araxava conquered much of Northern India. By 175, all of North India from Sindh to Bengal was under the control of the Araxavanid Empire. Buddhism in India was revived by the Araxanvanids. This is the beginning of Indo-Persian culture, which still exists today.
Greek missionaries had at last made their way from Slavic Eastern Europe into the Scandinavian Peninsula and Jutland. The Vikings, who were beginning to expand, were converted to Islam, being one of the only Germanic groups to convert to Islam, with the other being the Anglo-Saxons, who were converted by the Vikings. The Norse Golden Age was beginning. With their conversion, a large amount of Greek vocabulary entered their language. The Vikings would expand into the New World before 500.
Collapse of the Frankish Empire
The Merovingian Franks had already reached a cultural zenith. The empire was collapsing. The first region to declare independence was the Duchy of Aquitania in 182. The region was lawless until a duke was installed. This resulted in most power to be in the duke's hands. The next region was the isolated Kingdom of Tolosa in 186. This region was far from the authority of Aachen. This resulted in an isolated region under the control of near-independent feudal lords. One of the lords declared independence and the others fell under his authority. Another region to fall away from the control of the Franks was Gaul. A major lord established the Kingdom of Gaul, although his kingdom was only the north of the Roman province of Gaul. Even Austria became independent, creating the foundation of the modern state. The Franks only had control over Italy and collapsed, breaking up Italy into several small states.