Towards the end of the Song Dynasty (960-1279), the imperial court was forced south by the formidable Jurchen people, who incorporated China’s northern territories into their Jin Dynasty (1115–1234). For over 100 years, China was split virtually down the middle, with the Jin Dynasty ruling the north and the Southern Song Dynasty (1127–1279) reigning over the south. Yet the Jurchens were nothing compared to the foes that the Song imperials would soon face. Little did they know that a forbidding figure, the likes of which the world had never seen, was amassing power on the northern borders.
In 1206, Genghis Khan united the Mongol and Turkic tribes of the northern steppes, earning him the title of “Great Khan”. With hordes of experienced soldiers at his back, he set out on a conquest that would soon become legendary. His lifetime achievement, the Mongol Empire (1206–1368), would come to be known as the largest contiguous land empire in history. In 1214, he stormed the Jin Dynasty and conquered several of their major cities.
Under the reign of his third son, Ögedei Khan, the Jin Dynasty and the Tangut-led Western Xia Dynasty (1038–1227) were finally annexed. With the north of China conquered, the Mongolians soon turned their gaze south. When Möngke Khan took the throne in 1251, he granted his brother Kublai control over Mongol-held territories in China. In 1259, Möngke suddenly died without a named successor. Soon, a civil war broke out between Kublai and his brother Ariq Böke over who was the rightful heir to the throne.
Before the civil war, the Mongol administration had struggled with governing the sedentary population of northern China. They were nomadic, and were unfamiliar with the practices of the Khitan, Jurchen, and Han Chinese people who occupied their new territory. They attempted to synthesise their Mongolian military administration with that of traditional Chinese bureaucracy, but this re-feudalisation was something that northern China’s citizens bitterly resisted. In short, China was being ruled much like a colony for the Mongolians and their allies, which caused civil unrest among the native people.
Kublai depended on the knowledge and resourcefulness of his Han Chinese subjects, so he modelled his bureaucracy on that of traditional Chinese dynasties in order to earn their respect. In the end, this was the edge he needed to defeat his brother in battle. By this time, the three western khanates (the Golden Horde, Chagatai Khanate, and Ilkhanate) only acknowledged Kublai as Great Khan nominally, but he was about to gain yet another prestigious title. In 1271, after a series of successful military campaigns in Sichuan province and the Yangtze River Basin, he proclaimed himself Emperor of the Yuan Dynasty.
On the advice of his Han Chinese counsellors, Kublai centralised the bureaucracy, expanded the circulation of paper money, and restored the main administrative structure of previous Chinese dynasties. After a series of southern military campaigns, Mongolian forces defeated the Song loyalists in 1279 and the last Song Emperor committed suicide. This officially brought an end to the Song Dynasty, and marked the point where the Yuan Dynasty re-united northern and southern China.
However, numerous wars and construction projects had drained the Mongol treasury, and Kublai faced significant financial difficulties. Corruption and scandal within the Mongol court meant that any efforts to raise and collect tax revenues were often thwarted. On top of this, the talented Han Chinese scholar-officials, who had served under the Song Dynasty, were often relegated to minor positions in government. This was primarily due to the establishment of the Four Class System.
After the fall of the Song Dynasty, Kublai Khan implemented a social caste system where all of his citizens were separated into four categories. The first class contained solely those of Mongolian ethnicity; the second class or semuren were associates of the Mongolians, such as the Turks or the Middle Eastern Muslims; the third class or hanren was made up of inhabitants from northern China who had been subjects of the conquered Jin and Western Xia dynasties; and the fourth class or nanren consisted of any former subjects of the Southern Song Dynasty. The term “social class” may be misleading, as these groups denoted degrees of privilege rather than wealth or social influence. For example, there were desperately poor members of the first class, and exorbitantly rich members of the fourth class. People were placed in these classes based on how early their empires had surrendered to the Mongolians, hence why the Southern Song ranked at the bottom.
However, this system unfairly stipulated that the four classes receive different treatment when it came to political, legal, and military affairs. For example, although all classes of people could become court officials, the higher ranks were granted solely to Mongolians and semuren, with very few positions being held by members of the third and fourth classes. Mongolians and semuren were also tax-exempt, and were able to receive lighter punishments for any crimes they committed. This discrepancy in the treatment of different ethnic groups created internal instability that was only manageable under a strong ruler, such as Kublai Khan. As soon as a weak or incompetent ruler took the throne, disintegration and the decline of the dynasty was inevitable.
Tragically Kublai’s named heir, Zhenjin, passed away in 1285. When Kublai finally died in 1294, there was much internal struggle over who should succeed him. In the end, Zhenjin’s third son ascended the throne as Temür Khan. Although Temür managed to continue much of his grandfather’s good work, his lack of experience when it came to governance meant that corruption firmly took root in the Mongol court. By the time his successor Külüg Khan came to the throne, there were serious problems within the administration. This was only further aggravated when Külüg introduced a series of reforms that plunged the government into considerable financial difficulties. On Külüg’s death in 1311, the Yuan Empire was severely in debt and civil unrest was widespread.
 This is often referred to as the Jurchen Jin Dynasty to avoid confusion with dynasties of the same name.