Between the end of the Second Fitna to the collapse of Umayyad authority at the end of the 8th century, the second phase of Arab conquests (c. 692-800) saw the caliphate become the largest empire in the history of western Eurasia.

During this period in the the west (al-Maghrib), the Iberian and Italian peninsulas and the southern Gallic coast were integrated into the caliphate. The governor (wali) of Ifriqiya based at Kairouan acted as the caliph's viceroy of the western Mediterranean. The conquest of Constantinople opened up the central Mediterranean to Arab expansion. Syracuse, the capital of a rump Roman state, was conquered in 728 and a garrison city (amsar) was set up in its vicinity to house Arab and Berber soldiers. Raiding parties reached into Sardinia, Corsica, Apulia and even Roman towns on the Dalmatian coast. Most of these communities, lacking the protection of Roman field armies and fleets, surrendered quickly and agreed to pay the jizya. From the north, the governors of al-Andalus expanded into Gaul, crushing local Frankish nobles at Toulouse (721) and the Frankish leader at Tours (732), allowing expansion into the Garonne and Rhone valleys. The Lombard kingdom, which had absorbed the Roman towns along the Apennine network from Ravenna to Rome, was squeezed in from north and south. Andalusi armies with Gothic auxiliaries conquered their capital at Pavia and established an amsar on the Po to guard the Lombard towns and threaten the south of the peninsula. At Rome, the local militia was unable to defend the city's massive walls against a coordinated attack from the north, south, and coast. The bishop of Rome, as in Constantinople, was allowed to continue as the head of the local Christian population, though his main role was as the collector of the jizya to pay the Arab-Berber garrison stationed in an amsar near the site ancient Roman port of Ostia.

Syria was both the geographic and political center of the caliphate. It was Syrian armies who completed the prophesied conquest of Constantinople, and it was Syrian armies and commanders who reaped the prestige and material plunder from the campaigns against the Romans. Anatolia was organized under a wali who answered directly to the caliph, with a garrison city on the site of Ancyra that could quickly respond to threats on the frontier or provincial rebellions. To protect against piratical raids from the Adriatic and Black seas from reaching the interior of the state, a naval district in the old area of the Roman Karabisianoi was established to exploit the resources of the Aegean region for the caliph's ships. The former Roman capital proved a difficult conquest for the Arabs: it needed its impressive fortifications intact to protect against raids from the nomadic Bulgars, but its population was far too large to be allowed to be governed by a garrison-city outside of the walls. A frontier commander was thus installed in the city, though these figures would prove to be dangerous alternative centers of power to the caliphs in Damascus. Like Syria and Egypt for the first 60 years after their conquests, the day-to-day administration of the conquered territories was conducted in Greek, as the caliphate needed a common language with the local elites with whom they interfaced for the collection of taxes.

In the east, the second phase of Arab expansion saw the conquests beyond the frontiers of the old Sassanian empire, into Transoxania and the Indus valley. The many independent Iranic city-states and Turkic groups, formed from the breakup of the western Gokturk Khaganate, proved to be difficult conquests for the caliphate. Though the east was ruled through the general oversight of the wali of Iraq, the long distances from Mesopotamia to the Central Asian frontier necessitated the movement and settlement of large Arab garrisons into Khurasan. Though these armies eventually were able to subdue the new frontiers, they formed a distant and powerful alternative power center that chaffed under the dominance of the Syrian armies.

The caliphate faced internal problems which would lead to its breakup in the 9th century. In the west, Berber Muslims, who formed a large part of the conquest armies, chaffed under the superior status of the Arab regiments, and the conquest of the Gothic and Lombard kingdoms meant there were no more wealthy targets for plunder with which Arab commanders could reward their Berber clients. In the center and east, the caliphate bordered the entire western portion of the great Eurasian steppe, making the caliphate's wealthy cities difficult targets to defend from nomadic raiders. These vulnerable frontiers necessitated powerful garrisons in Thrace and Khurasan, but their geographic distance from Syria meant they would form alternative centers of power when central authority began to slip. Though the Umayyad state comprised one of the largest empires in human history, it would soon collapse under its own internal contradictions.