The Mongol army started its conquest of Transoxiana in 1219, following a diplomatic debacle initiated by the governor of the city of Otrar, Inalchiq. By 1221, the Mongols had invaded and conquered Transoxiana and most of Khorasan, devastating the cities of Samarqand, Bokhara, Urgench, Neishabur, and Herat. When Jalal od-Din Mingburnu, the defeated Khwarazmshah of Iran, returned in 1223 from an exile in India and decided to restore his control of central Iran, the Mongol troops, under the command of  Sobodei and Jebe, followed him into Azerbaijan and the Caucasus. The western campaigns were for a while halted when Chingiz Khan died in 1229 and his succession was thrown into a major debate in the Mongol court.

Under Ogodei, Guyuk, and Mungke, Chingiz’s immediate successor, the Mongols conquered most of the Khwarazmian territories in Iran and Caucasus, and going northwards, reached and passed through the Russian Steppe. The Mongols also subjugated the Seljuks of Rum and bordered the territories of the Caliphate of Baghdad. In the dynastic struggles between the families of Ogedei and Tului over the control of the empire, Mungke was chosen as the emperor in 1251 and quickly proceeded to strengthen the position of the house of Tului. He thus dispatched his brother, Hulegu, to conquer the rest of Iran and West Asia and establish his rule over those regions. Transoxiana, however, was mainly included in the possessions of the Ulus of Cheghetei, the third son of Chingiz Khan.

Hulegu, the real founder of the Mongol dynasty of Iran, henceforth known as the Ilkhans, was an energetic and ruthless commander. Moving across northern Iran, he mobilized the Turkmens who lived in Transoxiana and now moved to Anatolia, eventually coming to destroy the Seljuks of Rum and establishing the Ottoman power in that region. The highland kingdom of the Nizari Ismailis (the Assassins) was destroyed in 1256 when Hulegu invaded Alamut and killed Rukn ol-Din Khurshah. The vast library of the Nizaris were burnt, except a few volumes rescued by Persian speaking scholars in the Mongol service. In 1258, following a successful conquest of Baghdad, Hulegu killed the last Abbasid Caliph, Al-Musta’sim bil-lah and thus put and end to the Abbasid Caliphate. Leaving his troops to attend the Quriltai that was determining the successor to his brother Mungke in 1259. These troops, however, were defeated in the decisive battle of Ain Jalut by the Mamluks, marking the western most extent of Mongol power in West Asia.

Upon the election of Qubilai Khan as the Great Khan, Iran, Iraq, the Caucasus and Anatolia were put effectively under the rule of Hulegu, although Hulegu and his descendents, known as the Ilkhans, always accepted a nominal suzerainty of the Great Khanate, which now was represented by the Yuan Dynasty of China, the descendants of Qubilai Khan. In fact, the early Ilkhans continued to inscribe their coins in the name of the Great Khan and only considered them the Ilkhan, or “viceroys” of the Great Khans. This was usually done to keep legitimacy through the Great Khanate, and to prevent other Mongol houses from impinging on the Ilkhan territories. In 1262, Hulegu returned to Iran, shortly afterwards having to deal with an attack by his cousin, Berke Khan, one of the leaders of the Golden Horde. Although he was successful in protecting his possessions, his further campaigns, including the planned invasion of northern Caucasus, were largely unsuccessful. Hulegu died in 1265, leaving the Ilkahante to his son, Abaqa.

Abaqa had to start his reign by fighting off rival Mongol princes, including Berke and Mungke Temur, as well as the Chaghataid-Ogodeid alliance from Central Asia which was planning to put Qaidu on the Ilkhan throne. Most of these, however, were put down by 1270, allowing Abaqa to focus on his western borders. By this time, Abaqa might have converted to Nestorian Christianity, as his close ties with the Crusader states, mostly against the Mamluks, make clear. This is also obvious from some of his coins which bear a cross and a declaration of Christian faith. Abaqa’s alliance with the Crusaders, as well as control of the Armenian kingdom of Cilicia and the Crusader state of Antioch, created major conflicts with the Mamluks. A large campaign in 1281 ended indecisively, with sick Mongol Khan returning to Iran before dying in 1282.

Abaqa’s successor, his brother Teguder, had earlier converted to Islam, taking the name of Ahmad. This new faith thus brought him into alliance with the Mamluks, against the Crusaders, and reversed the foreign policies of Abaqa. In the east, the tendency towards Islam put Teguder at odds with his uncle Qubilai Khan, who then supported Abaqa’s son, Arghun, to depose his uncle. In 1284, Arghun killed Teguder and ascended the Ilkhan throne.

Arghun Khan was a Nestorian Christian, and thus returned to the policies of his father Abaqa. He provided much support for the Crusader States, although this was not enough to stop Qulawun, the Mamluk Sultan, from over-running and taking over the Crusdader States by 1290. In Iran, and from his capital in Tabriz, Arghun had to deal with further threats from Transoxiana and the Caucasus, where the Cheghetei and Golden Horde claimants kept on pressuring him. Arghun, in general, tried to keep loyal to the Yuan Empire in China, the Great Khans of the Mongols, and thus keep his relatives from over-running his empire.

In 1291, Arghun was assassinated by one of his generals, Taghachar, and was succeeded by his brother, Gaykhatu. Gaykhatu’s reign is known as the most glorious of Ilkhanids, as he was a devout Christian and made many gifts to the Church. Legend has it that Gaykhatu’s extravagance emptied the treasury, requiring him to print paper-money, an idea that was imported from China. The paper-money was not accepted in Iran, which traditionally had a silver-based currency, with gold coins being used in both ceremonial basis, as well as the silver standard. Gaykhatu’s unpopular reign then descended into riots in many cities, resulting in his assassination, again instigated by Taghachar.

Baydu, the son of Tarqai, a brother of Abaqa, was the chosen ruler by Taghachar. A meek and affectionate person, he was known as sympathetic to both Muslims and the Christians, and at the same time kind to his enemies. Among these was Arghun’s son, Mahmoud Ghazan, who was supported by Noruz, the powerful Mongol commander who had converted to Sunni Islam. Noruz made it a condition of his support for Ghazan for the latter to convert to Islam, and in 1295, the pair defeated Baydu after only a few months of reign. Baydu was executed and Ghazan ascended the throne.

The reign of Mahmoud Ghazan Khan, the son of Arghun Khan, was the golden age of the Ilkhanate. The new khan was a multi-lingual diplomat with deep interests in state craft and a thorough knowledge of economy and fiscal policy. He chose Khaje Rashid ol-Din Fazlollah, a Jewish convert to Islam, as his vizier, and the two managed to organize the administration of the Ilkhanate from an ad hoc basis to a centralised and prosperous one. Although like his predecessors, Ghazan Khan had to fight his Mongol cousins from the houses of Cheghetei and the Golden Horde, he was nonetheless rather secure in his rule. An early debacle, caused by the zealous policies of Amir Noruz, consisting of the destruction of Christian churches, was defused by Ghazan when he executed the Amir and exiled his followers, further excusing the Christians of paying the jizya tax.

Ghazan Khan’s efforts in coinage included the introduction of a silver based, bi-metallic coinage with new legends declaring only the name of the Khan, and omitting that of the Great Khan. His Ghaz Begi dinars became the standard of silver coinage for the next hundred years and were the most valued means of trade in Iran and the neighboring regions. He also built roads and caravanserais, and organized the postal system, as well as funding the building of the observatory of Maragha. In foreign policy, he diffused the threat of the Cheghetei Khanate, but had to face the Mamluks in Syria. The forces of Ghazan were supported by that of Hethum II of Cilicia, an Armenian vassal of Ghazan, and were allied with the remainders of the Crusader States. Initially successful, the Mongols managed to invade down to the Jordan Valley and take over most of Syria. A delegation asking for peace was sent to the court of Ghazan by the Mamluks, although the negotiations were unsuccessful. A final engagement, in 1303, called the Battle of Marj al-Saffar, saw a strong Mamluk defeat of the forces of Ghazan. Ghazan Khan died shortly after in 1304, leaving the prosperous Ilkhan domains to his brother, Mohammad Khodabandeh Oljaitu.

Oljaitu Khan was initially baptized as a Christian, named Nicholas after Pope Nicholas IV. However, like most Mongols, he seems to have had quite lax attitudes towards religion, later believing in Buddhism, before converting to Islam. Even in this, he was quite easy going, moving between various sects, including supporting the Shi’ite theologian, Allameh Helli. In continuing the usual Ilkhan policy of invading Syria, Oljaitu sent several embassies to the various Christian kingdoms of western Europe, looking for support. His promises seem to have been real enough to tempt Philip IV of France to want to rise for a new Crusade, although none of these in fact ever came to fruition. He did, however, marry a daughter of Andronikos II of Byzantium and helped him cope with the early rise of the Ottomans to power. The increased connections with Europe, including the several embassies sent, brought enough information about Europe to Iran for Rashid od-Din Fazlollah to compose the first ever Persian work of history which also covered the history of Europe.

Oljaitu died in 1316, leaving the throne to his son, Abu Sa’id Bahador Khan. The first Ilkhan with a non-Mongolian name, Abu Sa’id initially proved himself to be a worthy military commander. However, faction within the kingdom was on the rise, and independent movements such as the Sarbedariyyeh movement in Khorasan were threatening to cause a disintegration of the Ilkhanate. Rashid od-Din Fazlollah was executed through the instigation of the courtiers, who themselves then rose up to the position of power and started carving pieces of the kingdom to establish their own powers. From the northeast, the Golden Horde ruler, Uzbek Khan, was again attacking the Transoxianan borders of the Ilkhanate, although he was roundly defeated by Amir Chopan, Abu Sa’ids minister and military commander. As a way of ending the conflict with the Mamluks, Abu Sa’id was forced to sign the treaty of Aleppo with them in 1322, leaving the area west of the Euphrates to the Mamluk power.

East of the Euphrates, however, a Mongol commander, Hasan Jalayeri, known as Shaikh Hassan Bozorg (the Great Shaikh Hassan) was busy establishing his power. His main rival in the Ilkhanid court, Amir Chopan, was also his father-in-law. The competition between the Jalayerid and Chopanid houses eventually resulted in a disastrous partition of the Ilkhanid territories. In 1335, upon Abu Sa’id’s death, the Ilkhanate was already in deep decline.

Arpa Khan, Abu Sa’id’s successor, was a distant relative of the Ilkhans, descended from Arigh Bugha, a brother of Hulegu. He managed to defeat the Golden Horde under Uzbek Khan, but was himself killed in a fight against his rivals who then installed Musa, a grandson of Baydu, on the throne. Musa ascended the throne in 1336 as a puppet of Ali Beg, the governor of Baghdad. However, Shaikh Hassan Bozorg, the Jalayerid nobleman, defeated Ali Beg and soon removed Musa from power. The candidate of Shaikh Hassan Bozorg, Mohammad Khan, was challenged by several other Ilkhanid claimants. In the meantime, the son of Amir Chopan, Shaikh Hassan Kochak (the Little Shaikh Hassan) opposed the Jalayerid ruler and became a kingmaker of his own, defeating Shaikh Hassan Bozorg in several battles and confining him to Baghdad. Although Shaikh Hassan Bozorg chose another Ilkhanid pretender as his candidate for the throne, the Jalayerids soon started to rule on their right, forming a strong power based on Baghdad and expanding to western Iran, as far as Shiraz. The Ilkhanids were effectively finished in 1339, marking over a century of Mongol rule in Iran.