Islam Spreads East
Between the 630s and the middle of the seventh century, the armies of the new Muslim state in Arabia swept out of the peninsula and overturned the political map of western and central Asia. Within about two decades they had destroyed the Sasanian Persian Empire and pushed toward Central Asia, bringing Islam to the edges of the Indian subcontinent and the sphere of Tang China. The date of 630 is a convenient marker rather than a precise starting point, and the story unfolded gradually over many decades.
The background lay in the exhaustion of the region's two great powers. Byzantium and Sasanian Persia had fought a ruinous war that ended in 628, leaving both treasuries drained and their societies strained. At the same time, the Prophet Muhammad had unified much of Arabia under a new religious and political community. By the time of his death in 632, the Muslim state was a formidable force, and his successors, the early caliphs, turned that energy outward.
The campaigns against Persia moved quickly. Muslim forces defeated Sasanian armies at battles traditionally identified as Qadisiyya and Nahavand, in the late 630s and early 640s, and the Persian heartland came under Arab control. The last Sasanian king, Yazdegerd III, fled east and was killed around 651, ending the dynasty. Arab forces then advanced into Khorasan and the lands beyond the Oxus River, though the full conquest of Central Asia took much longer and met stiff local resistance. In the early eighth century, commanders such as Qutayba ibn Muslim made major gains around Bukhara and Samarkand, and in 751 Arab and Chinese-led forces clashed at the Battle of Talas.
Contact with India came first through the northwest frontier and the sea. Arab raids reached coastal regions and the borderlands of Afghanistan during the seventh century, and Muslim rule was established in Sindh in 711. Muslim merchants were also settling in ports along India's western coast, where trade was already ancient. Despite the title often given to this period, Islam did not spread as a single sweeping wave. Conquest, trade, migration, and gradual conversion all played roles, and historians debate how rapidly local populations adopted the new faith. In Persia, for example, Islam probably became the majority religion only after several centuries.
The consequences were lasting. Persia was absorbed into a Muslim world but kept its language and much of its culture, which later shaped Islamic art, literature, and statecraft. Central Asia became a crossroads where Islamic, Turkic, Persian, and Chinese influences met. In South Asia, the arrival of Muslim communities began a long process of cultural exchange that would transform the subcontinent's religious and political life in the centuries to come.