At first, the Mongols allied with Southern Song, 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 Northern Song capitals of Luoyang, Chang'an and Kaifeng from the Mongols and the Song had killed a Mongol
ambassador, the Mongols declared war on the Song. Very quickly the Mongol armies forced the Song back to the Yangtze, although the two sides would be engaged in a four-decade war until the fall of the Song in 1276.
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. The Mongol force which invaded
south China was far greater than the force they sent to invade the Middle East in 1256. The Mongols made heavy use of indigenous ethnic minority soldiers in southern China rather than Mongols. The
Kingdom of Dali's indigenous Cuan-Bo army led by the Duan royal family were the majority of the forces in the Mongol Yuan army sent to attack Song China during battles along the Yangtze river. During a Mongol attack against the Song China, there were only 3,000 Mongol cavalry at one point under the Mongol commander Uriyangkhadai, the majority of his army were native Cuan-Bo with Duan officers. While the Mongol forces had success against the non-
Han Chinese ruled 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. The fierce resistance of the Song forces resulted in the Mongols having to fight the most difficult war in all of their conquests, and the Mongols required every 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 various military advantages. Southern Song Chinese troops who defected and surrendered to the Mongols were granted Korean women as wives by the Mongols, whom the Mongols earlier took during their invasion of Korea as war booty. The many Song Chinese troops who defected to the Mongols were given oxen, clothes and land by Kublai Khan. As prize for battlefield victories, lands sectioned off as appanages were handed by the Yuan dynasty to Chinese military officers who defected to the Mongol side. The Yuan gave Song Chinese soldiers who defected to the Mongols juntun, a type of military farmland.
Chagaan (Tsagaan) and Han tumen General Zhang Rou jointly launched an attack on the Song dynasty ordered by
Töregene Khatun. After several indecisive wars, the Mongols unsuccessfully attacked the Song garrison at Diaoyu Fortress, Hechuan, when their Great Khan, Möngke, died of cholera or dysentery. However, the general responsible for this defense was not rewarded but instead was punished by the Song court. Discouraged, he defected to the Mongols and suggested to Möngke's successor, Kublai, that the key to the conquest of Song was the capture of Xiangyang, a vital Song stronghold. under Kublai Khan after the conquest of Southern Song dynasty. 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. Many
Han Chinese were enslaved in the process of the Mongols invasion of
China proper. According to Japanese historian Sugiyama Masaaki (杉山正明) and Funada Yoshiyuki (舩田善之), there were also a certain number of Mongolian slaves owned by Han Chinese during the
Yuan dynasty. However, there is no evidence that Han Chinese, who were considered people of the bottom of Yuan society according to some researchers, suffered particularly cruel abuse. 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 Song remnants remained. Chinese resistance lasted for a few more years as Song loyalists organized themselves around a powerless boy emperor, brother to the last formal Song emperor. In an attempt to restore the Song dynasty, several Song officials set up a government in
Guangdong, aboard ships of the vast Song navy, which still maintained over a thousand ships (which then carried the Song army, which had been forced by the Mongol army off of the land onto these Song warships). Realizing this, in 1279 Kublai sent his fleet to engage the Song fleet at the
battle of Yamen in the waters off of modern Hong Kong, winning a decisive victory in which the last Song
Emperor Bing of Song and his loyal officials committed suicide. This was the final major military confrontation of the Mongol conquest of the Song in southern China. However, members of the Song Imperial Family continued to live in the Yuan dynasty like
Emperor Gong of Song,
Zhao Mengfu, and
Zhao Yong. Zhao Mengfu painted at the Yuan court and was personally interviewed by Kublai Khan. This practice was referred to as
二王三恪, "Two Kings and Three Ke's." Historian
Patricia Buckley Ebrey noted that the Mongol
Yuan dynasty treated the ethnically Jurchen Wanyan royal family of the Jin Dynasty harshly, totally butchering them by the hundreds along with the
Tangut emperor of
Western Xia when they defeated him earlier. However, Ebrey notes that the Mongols were totally lenient with the Han Chinese Zhao royal family of the Southern Song, unlike the Jurchens treatment of the Northern Song in the
Jingkang incident. The Mongol armies spared the Southern Song royalty in the capital of Hangzhou, like
Emperor Gong of Song and his mother. Without sacking the city, they spared the civilians inside, allowing them to go about their normal business, and rehired Southern Song officials. The Mongols did not take the southern Song palace women for themselves but instead had Han Chinese artisans in Shangdu marry the palace women. The Mongol emperor Kublai Khan even granted a Mongol princess from his own Borjigin family as a wife to the surrendered Han Chinese Southern Song Emperor Gong of Song and they fathered a son together named Zhao Wanpu. ==Chinese resistance in Vietnam against the Mongols==