The Sassanian Empire enjoyed a newfound level of prosperity under the reforms of Khosrau I. It was engaged in frequent conflict with the Byzantine Empire on its western border, with sporadic raids by the White Huns in the north. The Byzantine Emperor Maurice, who had aided the new Sassanian Emperor Khosrau II whilst he was in exile, was killed in 602, which began a period of Sassanian expansion into Syria and Egypt. Although Khosrau II oversaw this success, he allowed it to weaken the state’s finances, which enabled the Byzantine emperor Heraclius (r. 610–641) to lay waste to much of Persia after assembling his remaining forces for a counterattack. Khosrau II was then overthrown in 628 and internal conflict struck the empire until young Yazdegerd III became emperor in 632. This period left the Sassanian Empire weak and may have been a factor in the success of the Arab invasion in 637 and consequent introduction of Islam.
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