The actions of Nadir corresponded with these declarations. He sent an officer to Constantinople, the duties of whose mission to the Emperor Mahmud were limited to this short message: "Restore the provinces of Persia or prepare for war." A messenger was deputed to Achmet, the Pacha of Bagdad, to apprise him that "the deliverer of Persia" was approaching. A peace had been concluded with the Russians, by which it was stipulated that they should abandon all the conquests they had made on the shores of the Caspian; and Nadir despatched two officers to that quarter to see that there was no delay in the execution of this treaty.
After adopting these measures Nadir marched to Ispahan. He first upbraided Shah Tamasp, and then pretended to be reconciled to him; but the scene of his mock submission to this Prince drew to a close. Tamasp was invited to the tents of his general to share in the joys of a feast, which terminated in his being seized and dethroned. He was sent to Khorasan. The Mahometan author who records these events is careful in informing us that the generosity of Nadir desired that Tamasp, though a prisoner, should be accompanied by all his ladies, and enjoy every other comfort that could be deemed necessary to pleasurable existence.
The time did not yet appear to Nadir to be ripe for his seizing the crown of Persia. The officers of his army and some venal nobles of the court earnestly requested that he, who was alone worthy to wear the diadem, would place it upon his head; but he rejected their entreaties, from pretended respect for the blood of the Suffavean kings. The son of Tamasp, an infant only eight months old, was seated upon the throne, and Nadir accepted the name and power of regent of the empire.
When the ceremonies necessary at this coronation were over, Nadir marched with a large army to the attack of Bagdad. The Governor of that city, Achmet Pacha, was not more distinguished for his talents as a soldier than a statesman; and the Persian leader had made his preparations in the expectation of an obstinate defence; but neither the valor nor skill of Achmet would have saved his city had not the Turkish general Topal Osman advanced, at the head of an immense army, to his relief. Nadir instantly resolved to hazard a battle. He left a small part of his army in his lines, and led the remainder to attack Topal Osman, who was encamped on the banks of the Tigris, near the village of Samarra, which is situated about sixty miles from Bagdad. The action that ensued was one of the most bloody ever fought between the Turks and Persians. It was at first favorable to the latter, whose cavalry put the enemy to flight; but the Turkish infantry advanced and restored the battle. A corps of Arabs, from whom Nadir expected support, fell upon one of his flanks. His men, who had been exposed all day to the intense rays of a summer sun, fainted with heat and thirst. He himself twice fell to the ground, in the midst of his enemies, from his horses being shot; and his standard-bearer, conceiving him slain, fled from the field. All these causes combined to give the victory to Topal Osman; and, after a contest of more than eight hours, the army of Nadir was completely defeated. The moment the news of this event reached Bagdad, the inhabitants of that city fell on the troops left to guard the trenches, who were also routed. The loss of the Persians in this battle was estimated by their enemies at sixty thousand men; and it probably amounted to more than one-third of that number. The Turks suffered almost as severely; but their triumph was very complete; for Nadir did not reassemble the whole of his broken and dispersed army till he reached the plains of Hamadan, a distance of more than two hundred miles from the field of action.