<td style="width:50%; border-right:1px dotted #aaa;">a) Total numbers unknown, over 30,000 in 1209b) Mongols - 90,000-120,000 Song Dynasty - 300,000 soldiers in 1234c) 180,000d) Over 450,000
</td><td style="width:50%; padding-left:0.25em">a) total numbers unknown, over 270,000 in 1209b) Over 1,000,000c) unknown, over 300,000d) Over 1,500,000
<td style="width:50%; border-right:1px dotted #aaa;">a) Unknownb) Moderately heavyc) Unknownd) Very heavy but fewer than Song
</td><td style="width:50%; padding-left:0.25em">a) Unknownb) Very heavyc) Unknown but very heavyd) Over 10,000,000 including civilians
The Mongol invasion of China spanned six decades in the 13th century and involved the defeat of the Jin Dynasty, Western Xia, the Dali Kingdom and the Southern Song, which finally fell in 1279. The Mongol Empire under Genghis Khan started the conquest with small-scale raids into Western Xia in 1205 and 1207. By 1279, the Mongol leader Kublai Khan had established the Yuan Dynasty in China and crushed the last Song resistance, which marked the onset of all of China under the Mongol Yuan rule. This was the first time in history that the whole of China was conquered and subsequently ruled by a foreign or non-native ruler, compared with the Manchus (who established the Qing Dynasty) who did so a few centuries later.
In the late 1190s and early 1200s, Temujin, soon to be Genghis Khan, began consolidating his power in Mongolia. Following the death of the Kerait leader Ong Khan to Temujin's emerging Mongol Empire in 1203, Keriat leader Nilqa Senggum led a small band of followers into Western Xia, also known as Xi-Xia. However, after his adherents took to plundering the locals, Nilqa Senggum was expelled from Western Xia territory.
Using his rival Nilga Senggum's temporary refuge in Western Xia as a pretext, Temujin launched a raid against the state in 1205 in the Edsin region. The Mongols plundered border settlements and one local Western Xia noble accepted Mongol supremacy. The next year, 1206, Temujin was formally proclaimed Genghis Khan, ruler of all the Mongols, marking the official start of the Mongol Empire. In 1207, Genghis led another raid into Western Xia, invading the Ordo region and sacking Wulahai, the main garrison along the Yellow River, before withdrawing in 1208.
In 1209, the Genghis undertook a larger campaign to secure the submission of Western Xia. After defeating a force led by Kao Liang-Hui outside Wulahai, Genghis captured the city and pushed up along the Yellow River, defeated several cities, and besieged the capital, Yinchuan, which held a well fortified garrison of 150,000. The Mongols, at this point inexperienced at siege warfare, attempted to flood out the city by diverting the Yellow River, but the dike they built to accomplish this broke and flooded the Mongol camp. Nevertheless, Emperor Li Anquan, still threatened by the Mongols and receiving no relief from the Jin Dynasty, agreed to submit to Mongol rule, and demonstrated his loyalty by giving a daughter, Chaka, in marriage to Genghis and paying a tribute of camels, falcons, and textiles.
After their defeat in 1210, Western Xia served as faithful vassals to the Mongol Empire for almost a decade, aiding the Mongols in their war against the Jin Dynasty. In 1219, Genghis Khan launched his campaign against the Khwarazmian dynasty in Central Asia, and requested military aid from Western Xia. However, the emperor and his military commander Asha refused to take part in the campaign, stating that if Genghis had too few troops to attack Khwarazm, then he had no claim to supreme power. Infuriated, Genghis swore vengeance and left to invade Khwarazm, while Western Xia attempted alliances with the Jin and Song dynasties against the Mongols.
After defeating Khwarazm in 1221, Genghis prepared his armies to punish Western Xia for their betrayal, and in 1225 he attacked with a force of approximately 180,000. After taking Khara-Khoto, the Mongols began a steady advance southward. Asha, commander of the Western Xia troops, could not afford to meet the Mongols as it would involve an exhausting westward march from the capital Yinchuan through 500 kilometers of desert, and so the Mongols steadily advanced from city to city. Enraged by Western Xia's fierce resistance, Genghis engaged the countryside in annihilative warfare and ordered his generals to systematically destroy cities and garrisons as they went. Genghis divided his army and sent general Subutai to take care of the westernmost cities, while the main force under Genghis moved east into the heart of the Western Xia Empire and took Ganzhou, which was spared destruction upon its capture due to it being the hometown of Genghis's commander Chagaan.
In August 1226, Mongol troops approached Wuwei, the second-largest city of the Western Xia empire, which surrendered without resistance in order to escape destruction. In Autumn 1226, Genghis took Liangchow, crossed the Helan Shan desert, and in November lay siege to Lingwu, a mere 30 kilometers from Yinchuan. Here, in the Battle of Yellow River, the Mongols destroyed a force of 300,000 Western Xia that launched a counter-attack against them.
Genghis reached Yinchuan in 1227, laid siege to the city, and launched several offensives into Jin to prevent them from sending reinforcements to Western Xia, with one force reaching as a far as Kaifeng, the Jin capital. Yinchuan lay besieged for about six months, after which Genghis opened up peace negotiations while secretly planning to kill the emperor. During the peace negotiations, Genghis continued his military operations around the Liupan mountains near Guyuan, rejected an offer of peace from the Jin, and prepared to invade them near their border with the Song. However, in August 1227, Genghis died of a historically uncertain cause, and, in order not to jeopardize the ongoing campaign, his death was kept a secret. In September of 1227, Emperor Mozhu surrendered to the Mongols and was promptly executed. The Mongols then mercilessly pillaged Yinchuan, slaughtered the city's population, plundered the imperial tombs west of the city, and completed the effective annihilation the Western Xia state.
One of the major goals of Genghis Khan was the conquest of the Jin Dynasty, allowing the Mongols to avenge the earlier death of a Mongol Khan, gain the riches of northern China and to establish the Mongols as a major power in the Chinese world.
Genghis Khan declared war in 1211, and while Mongols were victorious in the field, they were frustrated in their efforts to take major cities. In his typically logical and determined fashion, Genghis and his highly developed staff studied the problems of the assault of fortifications. With the help of Chinese engineers, they gradually developed the techniques to take down fortifications. Islamic engineers joined later and especially contributed counterweight trebuchets, "Muslim phao", which had a maximum range of 300 meters compared to 150 meters of the ancient Chinese predecessor. It played a significant role in taking the Chinese strongholds and was as well used against infantry units on the battlefield. This eventually would make troops under the Mongols some of the most accomplished and most successful besiegers in the history of warfare.
As a result of a number of overwhelming victories in the field and a few successes in the capture of fortifications deep within China, Genghis had conquered and consolidated Jin territory as far south as the Great Wall by 1213. He then advanced with three armies into the heart of Jin territory, between the Great Wall and the Yellow River. With the help of Chenyu Liu, one of the top officers who betrayed Jin, as well as the Southern Song, who wanted revenge on Jin, Genghis defeated the Jin forces, devastated northern China, captured numerous cities, and in 1215 besieged, captured and sacked the Jin capital of Yanjing (modern-day Beijing). However, the Jin emperor, Xuan Zong, did not surrender, but moved his capital to Kaifeng. There, his successors were eventually defeated in 1234.
Möngke Khan dispatched Kublai to the Dali Kingdom in 1253 to outflank the Song. The Gao family, dominated the court, resisted and murdered Mongol envoys. The Mongols divided their forces into three. One wing rode eastward into the Sichuan basin. The second column under Uryankhadai took a difficult way into the mountains of western Sichuan. Kublai himself headed south over the grasslands, meeting up with the first column. While Uryankhadai galloping in along the lakeside from the north, Kublai took the capital city of Dali and spared the residents despite the slaying of his ambassadors. The Mongols appointed King Duan Xingzhi as local ruler and stationed a pacification commissioner there. After Kublai's departure, unrest broke out among the Black jang. By 1256, Uryankhadai, the son of Subutai had completely pacified Yunnan.
During their campaigns, the Mongol Empire recruited many nationalities in their warfare, such as those of Central and East Asia. The Mongols employed Chinese troops, especially those who worked catapults and gunpowder to assist them in other conquests. In addition to Chinese troops, many scholars and doctors from China accompanied Mongol commanders to the west.
During the invasion of Transoxania in 1219, along with the main Mongol force, Genghis Khan used a Chinese specialist catapult unit in battle. They were used in Transoxania again in 1220. The Chinese may have used the catapults to hurl gunpowder bombs, since they already had them by this time  (although there were other siege engineers and technologies used in the campaigns too). While Genghis Khan was conquering Transoxania and Central Asia, several Chinese who were familiar gunpowder were serving with Genghis's army. "Whole regiments" entirely made out of Chinese were used by the Mongols to command bomb hurling trebuchets during the invasion of Iran. Historians have suggested that the Mongol invasion had brought Chinese gunpowder weapons to Central Asia. One of these was the huochong, a Chinese mortar. Books written around the area afterward depicted gunpowder weapons which resembled that of China.
One thousand northern Chinese engineer squads accompanied the Mongol Khan Hulagu during his conquest of the Middle East. 1,000 Chinese participated in the Siege of Baghdad (1258). The Chinese General Guo Kan was one of the commanders during the siege and appointed Governor of Baghdad after the city was taken. But this is probably wrong since Hulagu's associate, Nasir al-Din Tusi claims that the darugha was a certain Asuta Bahadur or according to Rashid and Bar Heabreus, Ali Bahadur who repulsed the Mamluk charge under the shadow Caliph in 1262.
At first, the Mongols allied with Song China as both had a common enemy in the form of Jin. However, this alliance broke down with the destruction of Jur'chen Jin in 1234. After Song forces captured the former Chinese capitals of Luoyang, Chang'an and Kaifeng from the Mongols and killed a Mongol ambassador, the Mongols declared war. Very soon, the Mongol armies had forced the Song back to the Yangtze, and the two sides would be engaged in a four-decade war until the fall of the Song in 1276.
While the Mongol forces had success against the non-Han Chinese states of the Jin and Xia, conquering the Song took much more time. The Song forces were equipped with the best technology available at the time, such as an ample supply of gunpowder weapons like fire lances, rockets and flamethrowers. However, intrigues at the Song court would favour the Mongols. The fierce resistance of the Song forces resulted in the Mongols having to fight the most difficult war in all of their conquests. The Chinese offered the fiercest resistance of among all the Mongols fought, the Mongols required every single advantage they could gain and "every military artifice known at that time" in order to win. They looked to peoples they already conquered to acquire any military advantage.
After several indecisive wars, the Mongols unsuccessfully attacked the Song garrison at Hechuan when their Great Khan, Möngke, died of cholera or dysentery. However, the general responsible for this defence was not rewarded and instead punished by the Song court. Discouraged, he defected to the Mongols. He suggested to Möngke's successor, Kublai, that the key to the conquest of Song was the capture of Xiangyang, a vital Song stronghold.
The Mongols quickly enclosed Xiangyang and defeated any attempt to reinforce it by the Song.
After a siege that lasted several years, and with the help of Muslim artillery created by Iraqi engineers, the Mongols finally forced the city of Xiangyang to surrender. The dying Song Dynasty sent its armies against the Mongols at Yehue under the incompetent chancellor Jia Sidao. Predictably, the battle was a disaster. Running out of troops and supplies, the Song court surrendered to the Mongols in 1276.
With the desire to rule all of China, Kublai established the Yuan Dynasty and became Emperor of China. However, despite the surrender of the Song court, resistance of the Song remnants continued. In an attempt to restore the Song dynasty, several Song officials set up a government in Guangdong, aboard the vast Song navy, which still maintained over a thousand ships. Realizing this, Kublai sent his fleet to engage the Song fleet at the battle of Yamen in 1279, winning a decisive victory in which the last Song emperor and his loyal officials committed suicide. Following this, the Mongols established their rule over all of China. The Yuan Dynasty had ruled China for about a century, until the fall of Dadu in 1368.