Mongol Conquest of the Khwarazmian Empire

The Mongol invasion of Persia, also known as the Mongol conquest of Khwarezmia, was a Mongol invasion of the Khwarazmian Empire led by Genghis Khan and Hulagu Khan. The Mongol conquest of Central Asia and the Islamic world began with the thorough defeat and destruction of the Turo-Persian Empire at the hands of the Mongols. When Shah Muhammad II, the Shah of Khwarazm, breached a peace deal with Genghis Khan, the series of events that led to the Mongol invasion began.  The governor of the city of Otrar seized and executed all members of a Mongol trading caravan on the Shah's orders; when the Khan sent three diplomats to the Shah at Urgench to avert open conflict, one was killed, and the others were publicly humiliated. Genghis quit the wars he was fighting in China and prepared to attack Khwarazm, outraged by this insult. The Mongol army decimated the Shah's dominion in the ensuing conflict, which lasted less than two years. Genghis Khan led 100,000 warriors into the Khwarazmian Empire, exploiting existing weaknesses and conflicts to isolate and destroy his enemies. The people of Merv and Nishapur in western India were killed in one of the deadliest battles in human history. in contrast, the three most important Eastern Kwarazmian cities (Bukhara, Samarkand, and Urgench) were successfully besieged and ravaged. Shah Muhammed, dissatisfied with the Mongol Empire's concessions in his kingdom, died on an island in the Caspian Sea. The Mongol conquest of Central Asia's Khwarazmian heartlands served as a springboard for the Mongol conquests of the Caucasus and the Abbasid Empire. The powerful Ilkhanate would control much of the Khwarazmian areas conquered by Genghis. The Chagatai Khanate ruled some of the northern lands when the Empire later broke into four distinct khanates. Timur would commence his large-scale assaults against the remainder of Asia from these northern areas.

After defeating the Kara-Khitans, Genghis Khan's Mongol Empire obtained a border with the Khwarezmid Empire, ruled by Shah Ala ad-Din Muhammad. The Shah had only recently gained control of some of the country, and he was also embroiled in a feud with the Caliph An-Nasir. The Shah had refused to pay tribute to the Caliph as Islam's titular head and demanded recognition as Shah of his dominion without any of the usual bribes or pretences. This had caused him troubles on his southern border alone. The rapidly expanding Mongol Empire made touch at this point. According to Mongol historians, the great Khan had no intention of conquering the Khwarezmid Empire at the time and was primarily interested in trading and possibly allying. The Shah was sceptical of Genghis' desire for a trade arrangement. Reports from the Shah's embassy in China, Zhongdu (Beijing), highlighted the Mongols' ferocity in assaulting the city during the Jin dynasty battle. It's also worth noting that the Caliph of Baghdad attempted to start a war between the Mongols and the Shah a few years before the Mongol invasion. Nasir and the Shah quarrelled, prompting this attempt to ally with Genghis Khan.  Still, the Khan had no interest in allying with any ruler who claimed ultimate authority, whether titular or not and thus marked the Caliphate for extinction by Genghis' grandson, Hulegu. This attempt by the Caliph coincided with the Shah's continued claim to the title of the sultan of Khwarezm, which Nasir refused to grant since the Shah refused to recognize his power, however fictitious it was.

However, Genghis rejected the idea of battle since he was at war with the Jin dynasty and making a lot of money through trading with the Khwarezmid Empire. Genghis then dispatched a 500-man Muslim caravan to Khwarezmia to establish official trading relations. However, Inalchuq, the Khwarezmian city of Otrar, detained members of the Mongolian caravan, alleging that the caravan was a plot against Khwarezmia. He executed the entire caravan with Sultan Muhammad's permission, and the caravan's goods were sold at Bukhara. Any members of the trade delegation, however, seem unlikely to be spies. It's also unlikely that Genghis was using the caravan to provoke a fight with the Khwarezmid State, given that he was making steady headway against a faltering Jin empire in northern China at the time. Genghis Khan subsequently summoned the Shah, who dispatched the second party of three diplomats (one Muslim and two Mongols) to demand that the caravan at Otrar be released. The governor was handed over for punishment. Before sending the Mongols back to Genghis Khan, the Shah had both shaved, and the Muslim beheaded. Muhammad also ordered the caravan's personnel to be killed. This was taken as a serious insult by the Khan, who regarded diplomats as "holy and inviolable." As a result, Genghis Khan launched an invasion of the Khwarezmian Empire. In 1219, the Mongols crossed the Tian Shan Mountains and entered the Shah's dominion.

After gathering information from many intelligence sources, mainly spies along the Silk Road, Genghis Khan meticulously prepared his army, which was organized differently than his previous campaigns. The adjustments came in, adding support units, both heavy and light, to his dreaded cavalry. Genghis assimilated numerous characteristics of Chinese combat, particularly in siege warfare, while still relying on the conventional advantages of his mobile, nomadic cavalry. Battering rams, gunpowder, and massive siege bows capable of shooting 20-foot (6 m) arrows into siege structures were among the items in his luggage train. The Mongol intelligence system was very strong. The Mongols never invaded a country that hadn't been carefully scouted in terms of a military and economic will and ability to resist.  Subutai and Batu Khan, for example, scouted central Europe for a year before annihilating the armies of Hungary and Poland in two different wars two days apart. The Khan exhibited indirect attack for the first time in this invasion, which would become a trademark of his following campaigns and those of his sons and grandsons. The Khan separated his army and dispatched one force specifically to find and execute the Shah, forcing him to flee his land. The Shah's armies were defeated piecemeal by the Mongol army, who began the total devastation of the kingdom that would characterize many of their later conquests. With around 200,000 direct men (mainly city garrisons) in his army, the Shah also had many people in surrounding cities in case they were needed. The Empire had only recently captured much of its land, and the Shah was afraid that if his army were grouped under one command structure, it would be turned against him. Furthermore, reports from China to the Shah showed that the Mongols were not skilled in siege warfare and had difficulty taking fortified locations. As the campaign progressed, the Shah's troop deployment decisions would prove devastating, as the Mongols' speed, surprise, and tenacity prevented the Shah from efficiently deploying his forces.

Forces

The estimated sizes of opposing armies are sometimes disputed. However, all contemporary and near-contemporaneous sources (at least those that have survived) agree that the Mongols were the numerically superior force. Several chroniclers, including Rashid Al-Din (a Mongol Ilkhanate historian), provide estimates of 400,000 for the Shah (distributed throughout the Empire) and 600,000 or 700,000 for the Khan. In his Tarikh-i Jahangushay, the contemporary Muslim writer Minhaj-i-Siraj Juzjani also gives Genghis a Mongol army size of 700,000 to 800,000 men. However, modern historians are still debating whether or not these figures accurately reflected reality. Among others, David Morgan and Denis Sinor doubt the numbers are correct in absolute or relative terms. John Mason Smith, on the other hand, believes the figures for both armies are correct (While defending high-end figures for the Mongols and their adversaries in general, such as claiming that Rashid Al-Din was true when he said the Ilkhanate of the 1260s had 300,000 soldiers and the Golden Horde had 300,000 soldiers).

Sinor officers a figure of 400,000 for the Khwarezmians but only 150,000 for the Mongols. According to The Secret History, the Mongols had 105,000 warriors total (in the entire Empire, not only on a campaign) in 1206, 134,500 in 1211, and 129,000 (excluding some far-flung divisions) in 1227 of the Mongols, a Mongol source. For Khwarezm figures, there is no comparable reputable source. Carl Sverdrup estimates the Mongol army at 75,000 men based on various sources and estimating methods. Sverdrup likewise estimates the Khwarezmian army to be 40,000 men (excluding specific city-restricted militias) and underlines that, at the very least, all contemporary sources agree that the Mongol force was the greater of the two. He claims to have arrived at 40,000 by first calculating the size of the Mongol army based on historical records and then assuming the Kwharezmian army was exaggerated to about the same magnitude by both pro-and anti-Mongol historians Rashid Al-Din and anti-Mongol chroniclers such as Juzjani. McLynn also believes that 400,000 is an exaggeration and 200,000 is a more accurate figure (including garrisons).  He estimates that out of a total Mongol strength of 200,000, 120,000 will be effective (including troops nominally on the campaign but never engaged, and those in China).  Apart from Muqali, Genghis enlisted the help of his most capable generals. Genghis also brought with him a significant number of foreigners, mostly of Chinese descent. These foreigners included siege specialists, bridge builders, doctors, and a wide range of speciality soldiers. A census was undertaken by Hulegu Khan of the same regions a few decades later provides the sole hard indication of the Empire's potential military might. Hulegu ruled nearly all of the former Khwarezmian empire's lands, including Persia, modern-day Turkmenistan, and Afghanistan, except for most modern-day Uzbekistan and Tajikistan, the region had had over 40 years to recover population-wise from the initial conquest. These fields were estimated to have a total capacity of five tümens.  Each tumen was meant to have 10,000 men in it, but they frequently only had 5,000. If Hulegu's census is correct, the former Khwarezmian regions could field 25,000 soldiers, putting Sverdrup's estimate of 40,000 warriors in all into perspective. Genghis Khan deployed a Chinese speciality catapult unit in battle with the main Mongol force during the invasion of Transoxania in 1219; they used it again in Transoxania in 1220. Because they already possessed gunpowder bombs, the Chinese may have utilized the catapults to launch them. Several Chinese skilled with gunpowder served with Genghis Khan's army as he conquered Transoxania and Persia. According to historians, the Mongol invasion transported Chinese gunpowder weapons to Central Asia. The Huo Chong, a Chinese mortar, was one of them.

Khwarezmian Weakness and Disunity

The Mongols benefited greatly from the Khwarezmian empire's frailty, in addition to probably outnumbering the Shah's force and almost certainly possessing more horses in total and more troops in practically every battle. While the Shah's realm was often portrayed as strong and united, most of his possessions were recent conquests that were only nominally pledged to him, to the point where the Shah didn't trust most of his army. As a result, he divided them into garrisons, commanded by local governors who functioned more or less independently. There was no effort to coordinate a grand strategy among the provinces or assemble many armies to fight the invaders on a single front.  Furthermore, many of the districts that Muhammad entrusted his troops with defending had recently been ravaged by the Shah's army. He passed through Nishapur in 1220, for example, and persuaded the citizens to repair the walls he had demolished when conquering the city years before. When the Mongols arrived, substantial sections of the Shah's army would fold with little or no combat due to the Empire's lack of cohesiveness. When Bukhara was invaded, Ibn al-Athir claims that most of the Khwarazmian army deserted and fled, leaving the now-weakly-defended colony to negotiate terms. When Samarkand was invaded later, the city's Turkic warriors, who had no loyalty to the Shah, reputedly declared of the Mongols: "Their race is ours. They are not going to kill us." After only four days of combat, they surrendered and handed the city over to the Mongols on the fifth day. Regardless, they were executed, along with a large portion of the city's population, much to their astonishment. Balkh's garrison surrendered peacefully. After seven days and a few minor forays (of only a few hundred soldiers apiece, according to the pro-Mongol Juvayni), Merv's garrison surrendered; they were also all executed, much to their surprise. Otrar, which held out for six months before being captured by the Mongols despite heavy casualties and a significant interruption for the Mongol military, and Urgench, where Ibn al-Athir demanded that Mongol losses beaten those of the defending soldiers for one of the few times during the war, were the only major cities known to have resisted the Mongols. The Shah's army's unreliability was possibly most crucial when his son Jalal al-cavalry Din's host crumbled due to defection because his Afghan and Turkic allies disagreed with him over-allocating war profits.  At the Battle of the Indus, his soldiers were severely depleted, allowing the Mongols to defeat him easily. With their network of spies, frequently supported by merchants who stood to benefit from Mongol dominance, the Mongols took full advantage of the situation and spread tales begging city dwellers to surrender.

Khwarezmian Structure

Another advantage for the Mongols was that Khwarezmia lacked fortifications compared to China, Korea, Central/Western Europe, and many other locations. Outside of the walls of large towns, there was no system of fortifications in most of the Empire, and even the most significant cities, such as Samarkand and Otrar, had mud-brick walls that Mongol siege engines could readily demolish. Rather than being tied down in dozens of tiny sieges or a single multi-year siege, as was the case in China, the Mongols could sweep through broad parts of the Empire and seize towns at pleasure in a short period. They had more trouble conquering Afghanistan, which possessed a fortress network; however, the Empire's relative lack of castles and the ease with which the Mongols conquered major areas meant that this didn't matter on a strategic level. The citadel of Ashiyar was besieged for 15 months before collapsing (requiring the attention of a large portion of the Mongol army), while Saif-Rud and Tulak suffered huge casualties before being conquered by the Mongols. Mötüken, Chagatai's favourite son, was killed during the siege of Bamyan. The Empire's urban population was concentrated in a small number of (by medieval standards) very great cities rather than many smaller towns, which facilitated the Mongols' conquest. On the eve of the invasion, the Empire's population was estimated to be around 5 million people, a small number given the vast region it encompassed. The Khwarezmian army had roughly 40,000 cavalries, the majority of whom were Turkic. Militias existed in Khwarezmia's major cities, but they were of poor quality, and the Shah struggled to muster them in time. With a combined population of around 700,000, the biggest cities had a total of 105,000 to 140,000 healthy males of fighting age (15–20 per cent of the population). Even so, only a small proportion of these would be members of a well-organized militia with adequate training and weaponry.

Even though they shared a border, the Mongol and Khwarezm empires were far apart from each other's homelands. Several dangerous mountain ranges lay between them, which the invader would have to cross. This campaign component is frequently ignored, yet it was a key factor in the Mongols' ability to establish a stronghold. The Khwarezm Shah and his ministers anticipated the Mongols would attack through the Dzungarian Gate, a natural mountain pass that connected their (now conquered) Khara-Khitai and Khwarezm Empires. Because Genghis would need months to assemble his army in Mongolia and march through the pass after the winter, one option for the Khwarezm defence was to advance beyond the Syr Darya villages and block the Dzungarian Gate an army. The Khwarezm decision-makers thought they'd have enough time to fine-tune their plan, but the Khan had attacked first. When the Khwarezm Empire declared war, Genghis promptly despatched instructions for a troop already in the west to cross the Tien Shan Mountains to the south and plunder the fertile Ferghana Valley in the east. Genghis' son Jochi and his top general Jebe led this smaller group of little more than 20,000–30,000 troops. The Tien Shan Mountain routes were far more dangerous than the Dzungarian Gate, and they tried the passage in the dead of winter, with almost 5 feet of snow on the ground. Despite their losses and exhaustion from the journey, the Mongols' arrival in the Ferghana Valley surprised the Khwarezm leadership and permanently took the initiative. This march can be compared to Hannibal's crossing of the Alps in Central Asia, and it has the same terrible results. The Shah had to use force to safeguard one of his most fruitful territories since he didn't know if this Mongol army was a diversion or their main army. As a result, the Shah deployed his elite cavalry reserve, preventing him from deploying with his main force somewhere else. While ravaging the valley, Jebe and Jochi appear to have kept their army in fine form, avoiding defeat by far larger force. The Mongols split up and manoeuvred across the mountains again at this point: Jebe marched farther south into Khwarezm territory. At the same time, Jochi took the majority of the force northwest to assault the Syr Darya's exposed cities from the east.

Otrar

Meanwhile, a Mongol force led by Chagatai and Ögedei descended from the north, perhaps via the Altai Mountains or the Dzungarian Gate, and laid siege to the border city of Otrar. Rashid Al-Din said that Otrar possessed a garrison of 20,000 soldiers. At the same time, Juvayni claimed 60,000 (horse riders and militia). However, like those given in most medieval chronicles, these estimates should be viewed with care, as they are likely overstated by order of magnitude given the city's size. Genghis Khan, who had marched across the Altai mountains, kept his main force closer to the mountain ranges and avoided engagement. According to Frank McLynn, this behaviour can only be described as Genghis laying a trap for the Shah. Because Shah chose to march his army up from Samarkand to fight Otrar's besiegers, Genghis quickly envelop the Shah's army from behind. The Shah, on the other hand, escaped the trap, forcing Genghis to alter his plans. Unlike most other cities, Otrar's governor did not march his troops out into the field to be annihilated by the numerically stronger Mongols, nor did Otrar's governor surrender after minimal fighting. Instead, the garrison stayed on the walls and fought back tenaciously, repelling numerous attacks. The siege continued for five months without success until a traitor within the walls (Qaracha), who had no loyalty to the Shah or Inalchuq, opened the gates to the Mongols, the prince's soldiers stormed the now-open gate and slaughtered the majority of the garrison. The citadel, which housed the remaining one-tenth of the garrison, held out for another month before being captured after massive Mongol casualties. Inalchuq fought to the last end, even scaling the castle in the final hours of the siege to throw down tiles at the advancing Mongols and slaying many of them in close-quarters combat. Many of the people were slaughtered by Genghis, the others were enslaved, and Inalchuq was executed.

The Mongol army was divided into five parts at this stage, each on opposite extremities of the opposing Empire. After the Shah failed to mount an active defence of the cities on the Syr Darya, Genghis and Tolui, with about 50,000 men, skirted the Syr Darya's natural defence barrier and fortified cities westwards siege to Bukhara first. To do so, they travelled 300 kilometres into the supposedly impenetrable Kyzyl Kum desert, hopping through the oasis and being guided for the most part by kidnapped nomads. As a result, the Mongols landed at Bukhara's gates, almost unnoticed. Many military strategists consider this unexpected entry into Bukhara to be one of the most successful military actions ever. Whatever Mohammed II had planned, Genghis Khan's manoeuvre across his back entirely seized his initiative and stopped him from carrying it out. The Khwarezm army could only react slowly to the Mongols' lightning-fast movements.

Bukhara

With merely a moat and a single wall, as well as the citadel typical of Khwarezmi cities, Bukhara was not well-defended. The Bukharan garrison, which was primarily made up of Turkic soldiers and led by Turkic generals, a breakaway attempt was made on the third day of the siege.  The city had 20,000 defenders, according to Rashid Al-Din and Ibn Al-Athir, although Carl Sverdrup thinks it only had a tenth of that number.  In an open fight, a breakaway army was annihilated. The city's officials let the Mongols in, but Turkic fighters defended the citadel for another twelve days. The Mongols highly respected artisans' skills. Thus they were spared from massacres during the conquests and instead forced to work as slaves for the rest of their lives. Survivors were executed after the citadel was seized, except for artisans and craftsmen deported back to Mongolia. Young males who had not previously served in the military were drafted into the Mongolian army, while the remainder of the populace was enslaved. A fire broke out when the Mongol forces looted the city, razing its majority to the ground.

Samarkand

Following the loss of Bukhara, Genghis Khan travelled to Samarkand, the Khwarezmian capital, where he arrived in March 1220. During this time, the Mongols also engaged in excellent psychological warfare, causing internal conflicts among their adversary. For example, the Khan's spies told them about the Shah's bitter feud with his mother, Terken Khatun. She supported some of the Shah's most senior commanders and his elite Turkish cavalry divisions. Because the Mongols and Turks were both steppe peoples, Genghis reasoned that Tertun Khatun and her army should join the Mongols in their fight against her son's betrayal.

Meanwhile, he organized for deserters to deliver papers claiming Tertun Khatun and several of her generals had joined the Mongols. This exacerbated the Khwarezm Empire's existing divides, making it more difficult for senior commanders to unite their forces. Genghis then added to the damage by issuing fraudulent decrees in the names of Tertun Khatun or Shah Mohammed, further tying up the Khwarezm command system, which was already tangled up. The Khwarezm generals, including the Queen Mother, were defeated as a garrison due to the Mongol strategic initiative, quick moves, and psychological methods. In comparison to Bukhara, Samarkand had many superior defences and a larger garrison. The city's defences are credited with 100,000–110,000 soldiers by Juvayni and Rashid Al-Din (both writing under Mongol auspices), while Ibn Al-Athir claims 50,000. Given the city's population of fewer than 100,000 at the time, several 10,000 seems more realistic. After completing the reduction of Otrar, Genghis' sons Chaghatai and Ögedei joined him, and the combined Mongol troops launched an assault on the city. Prisoners were used as body shields by the Mongols. The Samarkand garrison mounted a counterattack on the third day of warfare. Genghis drew about half of the soldiers outside the defences of Samarkand and murdered them in open combat while feigning withdrawal. The city was twice relieved by Shah Muhammad, but both times he was pushed back. All but a few soldiers surrendered on the sixth day. The remaining soldiers, all of whom were staunch followers of the Shah, defended the castle. Genghis reneged on his surrender terms when the stronghold fell and executed every soldier who had taken up arms against him in Samarkand. Many people were slain when the people of Samarkand were told to leave and gather in a plain outside the city. Genghis Khan tasked Subutai and Jebe, two of the Khan's senior generals, with tracking down the Shah at the time of the fall of Samarkand. The Shah had fled to a small island in the Caspian Sea with some of his most faithful warriors and his son, Jalal al-Din. In December 1220, the Shah passed away there. Most researchers blame illness for his death, but some blame the unexpected shock of losing his Empire.

Urgench

Meanwhile, Khwarezmian soldiers controlled the prosperous commercial city of Urgench. The Shah's mother had previously ruled Urgench, but she left when she learnt that her son had gone missing in the Caspian Sea. She was apprehended and sent to Mongolia. One of Muhammad's generals, Khumar Tegin, declared himself Sultan of Urgench. Genghis, Ögedei, and Chaghatai attacked from the south, while Jochi, who had been on a campaign in the north since the invasion, attacked from the north. Terken Khatun, Empress of the Khwarazmian Empire and "Queen of the Turks," was kidnapped by the Mongol army. The attack on Urgench was the most difficult of the Mongol invasion's battles. The settlement was developed in a marshy delta area along the Amu Darya River.

The soft-land made siege warfare difficult, and large stones for catapults were uncommon.  Regardless, the Mongols struck, and the city fell only after the defenders put up a brave fight, battling block by block. Due to the unusual difficulties of adapting Mongolian tactics to city battles, Mongolian casualties were higher than usual. The Khan's ongoing feud with his eldest son, Jochi, who had been promised the city as a prize, made the capture of Urgench much more difficult. Börte, Genghis Khan's teen bride and apparent lifelong love, was Jochi's mother, as was the case with his three siblings. Only her kids were considered Genghis' "official" sons and successors, not those conceived by the Khan's other 500 or more "women and consorts." However, Jochi was conceived amid controversy; during the Khan's early ascent to power, Börte was kidnapped and raped while imprisoned. Nine months later, Jochi was born. While Genghis Khan chose to recognize Jochi as his oldest son, there were long questions about Jochi's true origins. As Jochi participated in discussions with the defenders, seeking to persuade them to surrender so that as much of the city as possible remained undamaged, such tensions were present. This enraged Chaghatai, so Genghis avoided a family feud by choosing Ögedei as commander of the besieging soldiers just as Urgench collapsed. The removal of Jochi from command, as well as the sacking of a city he believed he had been promised, enraged him and drove a wedge between him and his ancestor and brothers, and is accredited with being a critical impetus for later actions of a man who saw his younger brothers promoted over him despite his considerable military skills.  The artisans were brought back to Mongolia, young women and children were sold as slaves to Mongol soldiers, and the rest of the population was killed, as was customary. According to the Persian scholar Juvayni, 50,000 Mongol soldiers were assigned to kill twenty-four Urgench civilians, totalling 1.2 million victims. While this is almost definitely an exaggeration, the sacking of Urgench is regarded as one of humanity's deadliest murders. The city of Gurgaon, south of the Aral Sea, was that destroyed. The Mongols broke the dams and drowned the city after it surrendered, then executed the survivors.

As the Mongols pounded their way into Urgench, Genghis sent his youngest son Tolui with an army into Khorasan's western Khwarezmid province. The power of Mongol arms had already been felt in Khorasan. The generals Jebe and Subutai had trekked through the area earlier in the battle the quest of the fleeing Shah. But, on the other hand, the territory was far from conquered; many significant cities remained ungoverned by the Mongols, and the country was rife with revolts against the tiny Mongol soldiers present, fueled by rumours that the Shah's son Jalal al-Din was assembling an army to battle the Mongols.  

Balkh

Tolui's army had roughly 50,000 men, with a core of Mongol soldiers (some estimates put it at 7,000) and a huge contingent of foreign troops, including Turks and previously captured peoples from China and Mongolia. Among the army's other features were "3,000 machines shooting heavy flaming arrows, 300 catapults, 700 mangonels to launch pots filled with naphtha, 4,000 storming-ladders, and 2,500 sacks of the earth for filling up moats."  As a result, Termez and Balkh were among the first cities to collapse.

Merv

The city of Merv was the first significant city to fall to Tolui's army. Merv was described by Juvayni as follows: "It dominated the territories of Khorasan in terms of territory, and the bird of peace and security hovered over its borders. Its chief men outnumbered the April raindrops, and its land competed with the heavens." Merv's garrison numbered around 12,000 soldiers, and the city had been flooded with refugees from eastern Khwarezmia. Tolui besieged the city for six days before assaulting it on the seventh day.

On the other hand, the garrison repelled the attack and launched their counter-offensive against the Mongols. Similarly, the garrison force was pushed back inside the city. Finally, on Tolui's promise that the people's lives would be spared, the city's governor surrendered the city the next day. Tolui, on the other hand, killed practically everyone who surrendered as soon as the city was handed up, possibly on a larger scale than Urgench.

Nishapur

Tolui moved west after defeating Merv, invading the cities of Nishapur and Herat. Nishapur fell in three days; here, Tokuchar, Genghis's son-in-law, was slain in battle. Tolui slaughtered everything alive in the city, including cats and dogs, with Tokuchar's widow presiding over the carnage. Herat submitted without a fight when Nishapur fell and was spared. During the Siege of Bamyan (1221), another scene of carnage was Bamian in the Hindu Kush, where strong resistance resulted in the murder of a grandson of Genghis Khan. The city of Toos came next. The Mongols completely ruled the province of Khurasan by spring 1221. Tolui returned east to meet his father after leaving the garrison forces behind.

The Shah's army was broken after the Mongol battle in Khorasan. After his father's death, Jalal al-Din gained authority and began gathering the remnants of the Khwarezmid army in the south of Afghanistan. Genghis had ordered men to track down Jalal al-assembling Din's army, and the two sides met in the spring of 1221 at Parwan. The Mongol army suffered a terrible defeat in this battle. Enraged, Genghis marched south and conquered Jalal al-Din on the banks of the Indus River. After being beaten, Jalal al-Din escaped to India. Genghis spent some time on the Indus' southern shore looking for the new Shah but was unsuccessful.  The Khan headed north, happy to leave the Shah in India. Genghis returned to Mongolia after destroying the remaining centres of resistance, leaving Mongolian garrison forces behind. The collapse and enslavement of the Khwarezmid Empire would be a portent of things to come for the Islamic world and Eastern Europe. The new area served as a stepping stone for Mongol armies during Genghis' son gender's reign to conquer Kievan Rus' and Poland, and subsequent battles took Mongol forces to Hungary and the Baltic Sea. The collapse of Khwarezmia left Iraq, Turkey, and Syria wide open to the Islamic world. Future Khans finally subdued all three of them. The fight with Khwarezmia also raised the crucial issue of succession. When the battle broke out, Genghis was not a young man, and he had four sons, each of whom was a fierce fighter with his band of loyalists. During the siege of Urgench, such sibling rivalry nearly came to a head, and Genghis was obliged to rely on his third son, Ögedei, to win the campaign. Following the defeat of Urgench, Genghis named Ögedei as his successor and decreed that future Khans would be descended from direct descendants of past rulers. Despite this, the four sons would eventually come to blows, demonstrating the fragility of Genghis' Khanate. Jochi never forgave his father and effectively withdrew from further Mongol conflicts, retreating to the north, where he refused to return to his father when summoned. Indeed, the Khan was planning a march on his wayward son at the moment of his death. The ensuing hatred was passed on to Jochi's sons, particularly Batu and Berke Khan (of the Golden Horde), who would conquer Kievan Rus. When Berke Khan, Genghis Khan's cousin (who had converted to Islam), invaded him in the Transcaucasus to advance the cause of Islam and Mongol soldiers were defeated, Hulagu Khan, one of Genghis Khan's grandsons via his son Tolui, was unable to revenge the setback.    The seeds of that warfare were sown during their fathers' quest for power with Khwarezmia.

The single-player campaign of Ensemble Studios' Age of Empires II computer game, published by Microsoft, features the Mongol conquest of Khwarezmia. On the other hand, the Mongols begin their invasion by assassinating the Shah in this video game. However, as traders, the assassins conceal themselves. The "Age of Mongols" bookmark begins with the grand strategy video game Crusader Kings II invasion.