Perhaps he felt that aggression was the very law of the Empire's being, since if the military spirit was once allowed to become extinct in the conquering nation, they would lose the sole guarantee of their supremacy.

At any rate, whatever his motive, we find him, after he had snatched a brief interval of repose, engaging in great wars both towards his eastern and his western frontier--wars which in both instances had results of considerable importance.
The first grand expedition was towards the East.

Cyrus, as we have seen, had extended the Persian sway over the mountains of Affghanistan and the highlands from which flow the tributaries of the Upper Indus.

From these eminences the Persian garrisons looked down on a territory possessing every quality that could attract a powerful conqueror.

Fertile, well-watered, rich in gold, peopled by an ingenious yet warlike race, which would add strength no less than wealth to its subjugators, the Punjab lay at the foot of the Sufeid Koh and Suliman ranges, inviting the attack of those who could swoop down when they pleased upon the low country.