Led by Genghis Khan, the Mongols defeated Kuchluk’s troops and established diplomatic relations with Sultan Mohammed II. The exchange of embassies took place while the sultan’s army was moving along the Syr Darya valley. Unexpectedly, it encountered a Mongol detachment led by Genghis Khan’s son Dzhuchi and Subedei-Bagatur, who pursued the Merkid tribe. Shortly thereafter, the ruler of Otrar, Inelyuk Kayir-Khan, with Muhammad’s permission, executed a detachment of Mongol traders, confiscating their goods. Having learned about the Otrar massacre, Genghis Khan demanded the extradition of Kayyr-Khan. But Kayyr-Khan was a representative of the Kipchak nobility, a nephew of the Sultan’s mother, the all-powerful Terken-Khatun, so Mohammed refused, killing Genghis Khan’s ambassadors. The great leader of the Mongols was furious and began to prepare a military campaign to destroy Khorezm Shah and his people.
Meanwhile, in Khorezm, disturbing stories about Mongol warriors were spreading, they were attributed unprecedented strength and endurance, they were said to have no number, but the most incredible stories concerned their conquest of the legendary «Altan Khan» — the Jin Empire in northern China. Court astrologers warned the sultan that the stars were not favorable to offensive action. But Muhammad did not want to attack. He distributed his army, which consisted of more than 400 thousand people and significantly exceeded the Mongolian quantitatively, to garrison the cities of Otrar, Fanakat, Bukhara, Samarkand and other fortresses along the eastern border. And he himself retreated south of the Syr Darya River, ordering his mother and wives to leave Khorezm for central Iran. Thus, the Mongol armies met no resistance in establishing their control over the entire Transoxiana (Arabic name for Maverannahr, the area between the Amu Darya and Syr Darya). Khwarizmshah’s troops were encamped in the besieged cities, and were annihilated one by one.
The first city the Mongols reached was Otrar, and its siege lasted five months. Avenging the lives of their traders, whose murder started the war, the Mongols spared no one, the entire population of the city, along with the ruler Kayir-Khan, was destroyed. Meanwhile, Genghis Khan sent his eldest son, Juchi, with the right wing of his troops to conquer the cities in the lower reaches of the Syr Darya, the left wing should capture the Fergana Valley, and he himself went with the main army to Bukhara and Samarkand. Bukhara surrendered on February 15, and Samarkand on March 16, 1220, only the Kipchak garrisons, who had settled in fortified fortresses, were completely destroyed. The cities were looted, many inhabitants were captured and used as human shields when storming other fortifications. Each captured city was obliged to pay tribute, and received a Mongol viceroy, a darugachi. Yelu Ahai was appointed Great Darugachi, based in Bukhara, he governed the whole of Maverannahr.
The surrender of Samarkand was a severe blow to Sultan Muhammad, who had expected the city to hold out for many months, if not years. Muhammad’s son, Jalal al-Din Mankburny, proposed to lead a counteroffensive by the armies of Khwarizmshah, but the sultan rejected his plan. After the fall of Samarkand, even elite Kipchak units belonging to his mother’s clan tried to assassinate the indecisive sultan. Muhammad fled through Nishapur farther and farther west, abandoning all desire to resist, and spent the spring of 1220 in utter despair.
After capturing Samarkand, Genghis Khan waited out the summer on the highlands near Bukhara, sending his best generals, Dzhebe-noyon and Subedei-Bagatur, with three tumen of horsemen (each with 10,000 men), in search of the Sultan. Crossing the Amu Darya in May 1220, they reached Balkh, which surrendered at their appearance. They appointed darugachi and followed the sultan’s trail westward. Everywhere, they spared cities that surrendered without a fight, appointed darugachi and moved on. But those towns that resisted were ruthlessly destroyed with all the inhabitants. Having succeeded in capturing the sultan’s mother Terken-khatun and the entire harem, they almost caught up with Muhammad in the mountains of Zagros in southwestern Iran, but he managed to escape to the north, to one of the islands of the Caspian Sea, where he died in the winter of 1220-1221. Djebe and Subedei proceeded north along the coast and, after defeating an allied army of Polovtsians and Russians, returned to Mongolia.
Soon, the cities that surrendered to Djebe and Subedei rebelled and killed the Mongol-appointed darugachi. With the arrival of fall, as the heat subsided, Genghis Khan began the second, more brutal phase of the war. He sent his vanguard, led by Toguchar, into eastern Iran and northwestern Afghanistan to destroy those he considered incorrigible rebels. Two middle sons — Chagatai and Ugedei — sent to connection with Djuchi, together they have destroyed capital of Khorezm the city Urgench in April 1221. Genghis Khan himself stormed the city of Termez on the Amu Darya, after which he crossed the river and razed to the ground the ancient city of Balkh, in which the Mongol darugachi was killed. At the same time, his younger son, Tolui, destroyed the city of Merv in March 1221, and in April of the same year left no stone unturned from Nishapur. Herat resisted for eight months, but did not escape the common fate. In all cities the Mongols spared only the artisans who were taken captive, the rest of the population was completely annihilated.
Meanwhile, Sultan Mohammed’s son Jalal al-Din, with great difficulty managed to reach the city of Ghazni in Afghanistan in February 1221. There he gathered the commanders and surviving detachments of his father’s army, with the help of which he managed to defeat three Mongol tumen under the leadership of Shiga Kutuku in the battle of Parwan, in the mountains of the Hindu Kush. However, soon after this victory, quarrels and mutual resentments greatly reduced the size of Jalal ad-Din’s army, and when Genghis Khan moved forward with the main forces of the Mongols, he again had to retreat. Only in November 1221 Genghis Khan pressed Jalal ad-Din to the Indus River, and he had to enter the battle, in which his army was completely destroyed. Jalal ad-Din himself managed to swim across the river and hide in India.
Unable to ferry his army across the fast and wide Indus River, Genghis Khan went upstream to Peshawar, while Ugedei turned back to raze the city of Ghazni to the ground. The unaccustomed climate and diseases irritated the Mongol army, it could not move quickly because of the huge wagons with looted valuables and prisoners, the number of which varied from 10 to 20 for each Mongol soldier. After a short rest Genghis Khan dealt with the excess prisoners and led the army back to the Hindu Kush mountains. In Afghanistan he remained with the main forces of his army until the spring of 1223, after which he returned to Mongolia. In this final phase of the war, clashes were constant, but resistance was unorganized and sporadic. Mountain fortresses in Afghanistan were besieged and their defenders slaughtered. A representative of the viceroy in Changchun, a Taoist who visited Genghis Khan in 1222-1223 describes «bandit» attacks and fires in the suburbs of Samarkand, as well as attacks on the pontoon bridge over the Amu Darya. Historical sources say almost nothing about these manifestations of popular resistance and guerrilla struggle, but it appears that they were widespread.
Persecution of Jalal al-Din.
Mongolian units were sent in pursuit of Jalal ad-Din, who hid in India and began to recruit Turkic and Afghan warriors under his banners. In 1224 through Baluchistan he again manages to penetrate into western Iran, where the surviving commanders of Khorezmshah tried to restore the army. In the following years Jalal ad-Din tried to create a new empire on the territory of western Iran and Armenia, fought with the rulers of Georgia, the Seljuk Turks and numerous fortress-states on the territory of Kurdistan. When Ugedei Khan became ruler of the Mongols after the death of his father in 1229, he dispatched Chormagan with three tumen of horsemen to finish off Jalal ad-Din. In August 1231 he was overtaken but managed to escape alone, only to be killed by some Kurdish highlanders. His recalcitrant Khorezmian troops, composed mostly of Kangyu tribes, retreated southward, where they joined the local armies.