During the later reign of the second emperor of the Sui Dynasty, Yang, the dynasty's authority began to wane. The main reason was the immense material and human cost of the protracted and fruitless attempts to conquer the Korean kingdom of Goguryeo. Coupled with natural disasters, the conscription of more and more men for the war and the hoarding of scarce grain reserves for the army's needs increased provincial discontent. As a result, from 611 on rural revolts broke out across the empire, and with the emperor's prestige and legitimacy diminished by military failure, ambitious provincial magnates were encouraged to challenge his rule. Yang nevertheless continued to be fixated on the Korean campaigns, and only as unrest spread within the Empire and the powerful Eastern Turks turned hostile