Another vital component of the army was the Armenian cavalry, which was recruited from outside the ranks of the Parthian "wuzurgan". However, the revolt of Armenia in 451 and the loss of its cavalry had weakened the Sasanian's attempts to keep the Hunnic tribes (i.e. the Hephthalites, Kidarites, Chionites and Alkhans) of the northeastern border in check. Indeed, Kavad's grandfather Yazdegerd II () had managed to hold off the Kidarites during his wars against them, which had occupied him throughout most of his reign. Now, however, Sasanian authority in Central Asia began to decay.