In the waning years of the Umayyad dynasty, a caliphal army suffered a major defeat in an area that is now part of Afghanistan, to a Turkish people called the Turgesh. The defeat was serious enough to disrupt caliphal control of the region called Transoxiana (literally “across the Oxus River,” which is today known as the Amu Darya) and allowed the Turgesh to advance into the eastern Iranian region of Khurasan. The setback for the caliphate was temporary–the Arabs laid a whupping on the Turgesh later that year that led to their almost total disappearance as a threat. The setback for the Umayyad dynasty, however, was considerably more significant, because the loss of direct control over Khurasan helped set the conditions that allowed the Abbasid revolution to incubate there.
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