 In the 3rd century, Kushan control fragmented into semi-independent kingdoms that became easy targets for conquest by the rising Iranian dynasty, the Sasanians (c. 224–561) which annexed Afghanistan by 300 AD.In these far off eastern-most territories, they established vassal kings as rulers, known as the Kushanshahs.Sasanian control was tenuous at times as numerous challenges from Central Asian tribes led to instability and constant warfare in the region.