The Muslim Civil War, sometimes referred to as the Umayyad Civil War or Abbasid Revolution, refers to the 40 years of open conflict between the Abbasid Caliphate and Umayyad Caliphate. The Umayyads were ruling over an empire that was primarily non-Arab and non-Muslim, which created great friction, which the Abbasids promised to fix (although they would suppress these groups even more). The revolution itself began when Abu Muslim of the Abbasid clan ignited a full scale revolt against the Umayyad dynasty in 747 on June 9. It spread throughout the already restless territories of the caliphate from its point of origin in northeastern Persia, and eventually the Abbasids captured all territory in the caliphate up to the Sinai Peninsula. However, the young Abd ar-Rahman I of the Umayyad clan was the sole survivor of the mass execution of the Umayyad royal family and moved the seat of government of the Umayyad Caliphate to the Maghreb in Kairouan in 753, where he succeeded in defeating the revolting Berber tribes and set up a government deemed "more fair" and unified the area around his rule. From there, he waged war against the Abbasids with the help of Al-Andalus until 787, eventually defeating them and restoring the Umayyad rule of much of the caliphate, leaving Abbasid rule confined to Persia and greater Khorasan.
The revolution began on June 9, 747, when Abu Muslim assembled a force of 10,000 and overthrew the Umayyad governor in Merv, who had recently but down a failed revolt carried out by disgruntled Shia Muslims who felt underrepresented and mistreated. Later, he and his commanders would go on to capture several Persian cities and eventually engage a massive Umayyad force directly and win a decisive victory at Gorgan, giving the Abbasids control over all of northern Persia. By the end of the year, the Abbasid army was strong enough to defeat 50,000 Umayyads at the Battle of Isfahan and establish a temporary government. Soon after these defeats, the Umayyads abandoned their remaining units in Khorasan, leaving them to be killed by the Abbasids. The few soldiers who remained loyal to the Umayyads in Khorasan were rounded up and beheaded by the Abbasids, ending Umayyad rule in Khorasan entirely and forcing the Umayyads to draw their attention away from the war with the Byzantine Empire. After his victories, Abu Muslim crushed any rebellions to his rule, and set his sights west.
The Abbasids entered Kufa in late 749, capturing the city and establishing governance. However, Umayyad commander Yazid ibn Umar al-Fazari set up a camp outside the city soon after and prepared to attack. Unfortunately for the Umayyads, the Abbasid forces noticed this and raided the camp, killing most of the soldiers there at the cost of their own commander's life. After this crushing defeat, al-Fazari fled west to Wazid, where he and the majority of other Umayyad reinforcements were trapped as the Abassids swept west and the Abbasid caliph As-Saffah was recognized in a Kufa mosque.
In early 750, the Abbasid armies sacked many cities throughout Iraq, eventually culminating in the Battle of the Zab along the Tigris River, sealing the fate of the Umayyad Caliphate. The Umayyad forces were thoroughly defeated beyond any usefulness, and just a month later the Abbasids stormed Damascus, executing much of the royal family and tracking others to Egypt were they were killed. However, one young prince survived, and went into hiding in eastern Maghreb. The Abbasids then assumed authority over the Islamic world with the seat of power in Baghdad.
The Civil War
After reaching Kairouan, the young Abd ar-Rahman I found himself surrounded with hostile enemies out for his blood. However, he was able to assemble an army in the Maghreb loyal to the Umayyads in 753, and defeat the warring Berber tribes that were fighting against both Abbasid and Umayyad rule. The emir of Al-Andalus at the time, Ayyub III, had very favorable views of the Umayyads and dispatched a sizable force into the Maghreb, helping to secure Umayyad rule in the region within months. Afterwards, the Berbers and other minorities were treated very fairly by the young Abd, and his territory came to like him by mid 754, and he was proclaimed caliph in a Kairouan mosque, catching the attention of the Abbasid dynasty, which immediately sent forces into his new caliphate to squash his pretension to the position of caliph.
Initially, the Abbasids made large gains, but the emir in Al-Andalus sent reinforcements and naval forces to halt them, allowing the Umayyad Caliphate to expand as far east as Barqah by late 758, from which point, the Andalusians were forced to turn their attention to the Holy Alliance due to an increasingly demanding war. By this point the new Umayyad Caliphate was able to stand on its own, and launched an invasion of the Abbasid Caliphate, pillaging its cities and disposing of Abbasid governors, which many Arab Muslims and some others had already come to dislike due to their massive policy changes from the previous leadership. In 763, Abd captured Alexandria and Fustat, rooting out any resistance to his rule and eliminating it, giving him a firm grip on all of North Africa.
The Abbasids had problems elsewhere, however, in the form of the Byzantine Empire and Khazar Khanate, which were waging war in the north. In 767, the Byzantine Empire sacked Damascus, creating mass chaos in the eastern caliphate, and enraging the Umayyads. The Abbasids were forced to relocate troops from the civil war to fight the Byzantine incursions, allowing Abd to invade the Sinai and Palestine, he himself leading forces that captured Jerusalem and Damascus in 768 and 770 respectively. At this point, many Muslims came to see the disasters facing the Abbasid Caliphate as punishment from Allah for their new and radical policies toward religious minorities, and several revolts broke out, further unraveling Abbasid power.
Abd ar-Rahman began ruling from Damascus in 773, and relocated a small force to fight the Byzantines in the north, pushing the, back into Anatolia within the year. In the meantime, the civil war had been all but won. The Umayyads regained Medina, Mecca, and other major cities. By 780, the Byzantines were forced back to their original borders and the Khazars had largely stopped their raids on the caliphate, keeping power firmly concentrated in Umayyad hands. The war had all but stopped by this time except for occasional raids on Baghdad and other Abbasid controlled cities, but in 787, the Umayyads sent a force of 30,000 to Baghdad, capturing it with ease and executing much of the Abbasid royal family, although a few escapes to Siberia, never to be seen again by the Umayyads (however, not gone from history). In Siberia, the Abbasids were able to convert some of the population and establish a small kingdom without the knowledge of much of the world.
After his great victory, Abd ar-Rahman I was venerated by the people of the caliphate as their liberator, even those who were non-Muslim, many of whom began converting at this time. The victory was not total, however, in the sense that the Grand War was still in full swing against the Islamic world. Although the Umayyads were war weary, they were ready to get behind their new caliph and protect Islam from perceived Christian assault. In the end, the caliphate had actually grown in size, due to the addition of the territory of several tribes in the Indian subcontinent under the Abbasids to generate income to fund the war. Abd treated these newcomers, as he did all people under his rule, equally except for the jizya on non-Muslims, unifying all the peoples in the caliphate and making it much more stable and easier to manage.
The Abbasid Kingdom of Sibir in southwestern Siberia was established in 798, and lost all contact with any states other than the local tribal peoples, whom they successfully converted in large numbers. The Umayyad Caliphate was passed down in Sibirian lore as a "devilish monstrocity" that loomed distantly to the south that was to one daybe conquered by those whom Allah viewed more favorably, and several generations passed without contact and with a deep fiery hatred for the Umayyad dynasty. Somewhere down the line, it was even believed by some that Abd ar-Rahman I was the devil himself.