While Nadir was employed in besieging Kandahar his generals had been successful in reducing the strongholds in its vicinity; and his eldest son, Reza Kuli, had, during this short period, obtained a fame which seemed to promise that his name would one day equal that of his father. The Afghan Prince of Kandahar had expected aid from the chief of Bulkh, against whom Nadir detached his son, with a chosen body of twelve thousand horse. The Prince not only defeated this ruler and took his capital, but passed the Oxus, and did not hesitate to give battle to the monarch of the Usbegs, who had advanced from Bokhara with an army far outnumbering the Persians. The rash valor of Reza Kuli was crowned with a signal victory; and the career of the young hero was only arrested by a mandate from his father, who desired him to recross the Oxus. Nadir at the same time addressed two letters to the King of the Usbegs, and to the other chiefs of that part of Tartary, informing them that he had sent orders to his son to retreat within the limits of the Persian empire, and not to disturb countries which were the inheritance of the race of Genghis Khan and of high Turkoman families. This conduct, which was evidently the result of that policy which affects moderation, that it may better accomplish its ambitious purposes, has been ascribed by some to a jealousy which they conceive Nadir, even at this early period, entertained of the rising reputation of his son; but those who impute it to this cause forget that Reza Kuli, when he returned, was not only received with extraordinary favor and affection, but soon afterward was intrusted with all the power of a sovereign, and left to govern Persia, while his father proceeded with his vast designs of subjugating to his authority the distant regions of India. When Nadir Shah marched against the Afghans he had sent an ambassador to Delhi requesting the monarch of India would give orders to the governors of his northern provinces not to permit the enemies of Persia to find a refuge from an avenging sword in the territories of an ally. No satisfactory answer had been received to this mission; and, while the Afghans were allowed to take shelter within the limits of the Indian empire, obstacles were thrown in the way of the return of the Persian envoy. Nadir, incensed at these proceedings, pursued the fugitives to Kabul, and not only made himself master of that city, but of all the country in its vicinity. After this conquest he addressed another letter to the Emperor of India, in which he reproached him, in the bitterest terms, for his past conduct, but still professed a desire of maintaining the relations of friendship. The bearer of this letter was slain by the Afghan chief: and Nadir, perhaps, did not regret an event which added to the pretexts that before existed to justify him to the world in undertaking the most splendid of all his enterprises--the invasion of India (1738).