The ordinary Mede, no doubt, lost something of his old daring and savagery; from disuse he became inexpert in the management of arms; and he was thus no longer greatly to be dreaded as a soldier.

But he was really not very much less brave, nor less capable of bearing hardships, than before; and it only required a few years of training to enable him to recover himself and to be once more as good a soldier as any in Asia.
But in the affairs of nations, as in those of men, negligence often proves fatal before it can be repaired.

Cyrus saw his opportunity, pressed his advantage, and established the supremacy of his nation, before the unhappy effects of Astyages' peace policy could be removed.
He knew that his own Persians possessed the military spirit in its fullest vigor; he felt that he himself had all the qualities of a successful loader; he may have had faith in his cause, which, he would view as the cause of Ormazd against Ahriman, of pure Religion against a corrupt and debasing nature-worship.

His revolt was sudden, unexpected, and well-timed.

He waited till Astyages was advanced in years, and so disqualified for command; till the veterans of Cyaxares were almost all in their graves; and till the Babylonian throne was occupied by a king who was not likely to afford Astyages any aid.