This chapter discusses three periods in the socio-economic history of Iran during the Mongol dominion, ranging from the twenties of the thirteenth century to the eighties of the fourteenth century. In the Middle Ages invasions by conquering nomads of cultivated settled areas were normally devastative. The Saljuq conquest of Iran was accompanied by pillage and destruction. The destructive nature of the invasion of Khurāsān by the Oghuz of Balkh in the fifties of the twelfth century is notorious. The Mongol conquest took an equally heavy toll in Tabaristān (Māzandarān). The reforms of Ghazan and the temporary transfer of a leading political role in the State from the nomad Mongol-Turkish aristocracy to the Iranian civil bureaucracy made some economic improvement possible, especially in agriculture. The Mongol conquest had a great and in general evil influence on the economic development of Iran; it had much less influence on the social structure of the country.