Large parts of the country were still under Ottoman and Russian occupation and the rest was in chaos and despair. Nader attacked and defeated the occupying Ottoman forces but had to postpone complete victory in order to turn his attention to the revolt of the Abdali Afghans in Herat, which he successfully quelled. While Nader was in Khorasan, Tahmasp, perhaps in an attempt to compete with Nader, violated the Perso-Ottoman ceasefire but was defeated and had to cede much of the territory which Nader had previously regained. Having returned to Isfahan in August 1732 Nader persuaded the army chiefs to replace Tahmasp by his infant son Abbas under his own vice-regency.
The renewal of war with the Ottomans eventually led to full victory and the peace of late 1733 whereupon the Ottomans agreed to withdraw from all the occupied lands; and when, a couple of years later, they tried to renege on the agreement, they were once again defeated and thenceforth kept the peace. In the meantime Nader also drove the Russians out of Iran by the 1735 treaty of Rasht.
In 1736 when the country was totally cleared of domestic chaos and foreign occupation Nader called a meeting in Dasht-e Moghan of chiefs and notables from all over Iran, ostensibly to decide the country’s regime but in fact to depose the Safavids and choose Nader himself as the Shah of Persia.
The conference participants knew their role well, but it would be a mistake to think that they took their decision merely or even mainly through fear and bribery. They offered Nader the crown, which he accepted on the condition that Iran revert to Sunnism, a wish which could not possibly be realized outside official formalities.
Nader was forty seven and had he then settled down to a long period of reconstruction he would have been worthy of much of the praise that Iranian governments and historians bestowed on him in the twentieth century. He was portrayed as a modern Iranian nationalist, a hero who had not only saved Iran from chaos and foreign occupation but had also brought the country fabulous riches and glory. Nader was in fact an illiterate Sunni tribesman whose mother tongue was Turkish and who saw himself as an Asian conqueror in the style of Amir Timur. His reign saw little peace, and he was given to cruelty, enslavement, pillage and slaughter, both inside and outside Iran. He was far from another Abbas I, with whom he has been unrealistically compared.
The first major act of the new shah was to lead an expedition against Qandahar in 1736, despite the fact that its ruler had acknowledged his sovereignty. Much of his baggage and equipment was carried by peasants whom he had enslaved in Kerman just for that purpose. He defeated the force that the ruler of Qandahar had sent to meet him, but had to camp for a long siege, and the city did not fall before March 1738. Following that, Nader attacked Mogul India on some flimsy pretext.
He had two interrelated motives for attacking India. Firstly, his wars had emptied the treasury, despite the imposition of heavy taxes, and he needed substantial funds to maintain his growing army. Secondly, he was, as he showed until the very end of his career, an obsessive conqueror who had to be on the move virtually all the time. Kabul fell first and Peshawar not long afterwards, and the Indian army was defeated at Lahore after stiff resistance. Then the Mogul emperor Mohammad Shah himself left Delhi to meet Nader in combat. They met at Karnal in February 1739: the Indians were defeated and Mohammad Shah surrendered to Nader.
Before returning to the Persian hinterland, however, Nader led his army to Bokhara and Khawrazm, and having defeated the rulers of Turkistan he conquered the whole of Transoxiana, which had not been part of a unified Persian empire since the Achaemenids. On his return, he moved the capital from Isfahan to Mashhad, which was closer to his Central Asian empire.