The period of Eastern Jin Dynasty and Sixteen Kingdoms was darkest and most chaotic era in Chinese history. In north of Yangtze River, there were more than 20 large and small regimes, which we collectively call "Sixteen Kingdoms." With exception of early Later Zhao, middle former Qin, and later Northern Wei, other regimes were small in size and limited in power. At that time, it was Eastern Jin dynasty that for a long time had an absolute advantage in terms of area, population and military affairs. The Eastern Jin Dynasty also organized four large-scale northern expeditions in a row, but why did it fail to unite North and South?

Ever since Western Jin Dynasty, Eight Kings Rebellion, and Yongjia Rebellion broke out in north, economy has been badly damaged and ethnic and class conflicts have been sharp. The south is relatively stable, so a large number of northerners prefer to move south. According to Tan Qixiang and others, there were about 900,000 registered households at time who decided to move south. The Western Jin royal family and aristocratic families also went south one by one and established Eastern Jin regime in south of Yangtze River.

A large number of people migrated to south, which provided sufficient labor for economic development of south. According to Ge Jianxiong's Population History of China,the population at beginning of Eastern Jin Dynasty reached 10 million people, which was basically same as in north; by late Eastern Jin Dynasty, population reached 17 million. , which is much larger than northern one. South migration has accelerated economic development of south. Relying on prosperous economy in south of Yangtze River, "wealth and prosperity" of Eastern Jin dynasty can fully support its great cause of unifying north.

However, Eastern Jin dynasty was not harmonious. First, Eastern Jin Dynasty was a single country in name, but in essence it was divided. Based on geographical division of Han Dynasty, south is divided into four major regions: Yangzhou, Yizhou, Jingzhou, and Jiaozhou. Yizhou was generally in a state of separatism under Eastern Jin Dynasty. There was a Chenghan regime in early days, and it was not restored until Huanwen period; Therefore, only Jingzhou and Yangzhou can really provide relatively stable support for Eastern Jin dynasty.

The contradiction between Jingzhou and Yangzhou is very noticeable. Yangzhou is capital of Eastern Jin Dynasty and foundation of country. In north of Yangzhou, there is a natural barrier of Yangtze River, which is a natural barrier for northern peoples going south. If northern peoples wanted to go south to attack Eastern Jin dynasty, they would inevitably attack upper reaches of Yangtze River first and then go downstream. Therefore, Jingzhou in upper reaches of Yangtze River became defense center of Eastern Jin dynasty. The military strength of Eastern Jin Dynasty in Jingzhou was very strong, "the most skilled soldiers made up half of imperial court."

Throughout Eastern Jin Dynasty, generals in Jingzhou had a "heart of defiance". Wang Dun, who first settled in Jingzhou, started Wang Dun Rebellion. Later, Tao Kan, Yu Liang, Yu Yi, Huang Wen, Huang Huo, Huang Chong, Yin Zhongkang, Huang Xuan, and others sat in Jingzhou and controlled military power upstream. In 403, Jiankang was defeated, proclaimed emperor, and title country was changed to Chu, so that Eastern Jin Dynasty effectively perished. From Wangdong uprising to Huangxuan uprising, Eastern Jin dynasty from very beginning to end was in quagmire of struggle between Jingyang and Yang, leaving country without additional forces to conduct Northern Expedition.

Warlords in Jingzhou and Yangzhou often used Northern Expedition to improve their reputation in order to gain throne. It also determined that Northern Expedition of Eastern Jin Dynasty was mostly limited to south of Yellow River and could not go deeper into Hebei. For example, Huan Wen's Northern Expedition recaptured Luoyang and invaded Guanzhong, but Huang Wen did not want to advance towards Chang'an because Huang Wen did not want to fall into quagmire of northern war and swallow up his military capital.

The second biggest controversy in Eastern Jin dynasty was controversy between Sima family and nobility, and controversy between southern nobility and northern nobility. The Jin family went south with support of northern and southern nobles. In early days of Nandu, northern nobles missed their homeland, so they wanted to reclaim north. However, southern nobles believed that Northern Expedition only absorbed wealth accumulated in south of Yangtze River, and even if north succeeded, southern nobles would not benefit much, so they did not support Northern Expedition. Under such conditions, Sima Rui could only seek stability and did not want to go to war. When Zu Ti proposed Northern Expedition, Sima Rui did not object, but did not support it either.

Geographic distribution of main clans of Jin Dynasty

When northern nobles acquired land in south of Yangtze River and built richer estates, they lost their desire to participate in Northern Expedition. The settlement of northern gentry in south, naturally, undermined power of southern gentry. At beginning of southern route, representative of southern gentry, who settled in south of Yangtze River, Zhou Qi raised an uprising, after which Zhou Xie, Xu Fu, Sun Bi, Zhou Xu and other nobles south of Yangtze River successively raised troops. After suppressing rebellion of southern nobles, Wang family from north destroyed two most powerful families, Yixing Zhou family and Wu Xingshen family, temporarily suppressing conflict between northern and southern nobles.

For Jin family, prosperity of any nobility would threaten them, so struggle between royal power and power of nobility in Eastern Jin Dynasty was also very fierce. For example, Xie group grew rapidly after Huan Wen's death, took control of government, and formed Beifu soldiers to defeat former Qin army and win Battle of Feishui. Thereafter, Xie's group took opportunity to launch Eastern Jin Dynasty's third large-scale Northern Expedition, and retook Henan and Shandong at one point. However, in order to limit Xie family, Sima Sima Tian group's clan took over command of Northern Army, and Northern Expedition Army was also withdrawn, and achievements of Third Northern Expedition were quickly destroyed.

Another serious contradiction in Eastern Jin dynasty was class contradiction between nobility and common people. During Jin Dynasty, a large number of civilians became dependent people, such as tenants, tribes, guests, slaves, etc. They basically lost their right to personal freedom, and aristocratic families even killed them at will. Under Jin Dynasty, about half of population became dependent people. After establishment of Eastern Jin Dynasty, this contradiction became more and more serious. At end of Eastern Jin Dynasty, Sima Yuan was forced into military service in Zhejiang area, which sparked largest peasant uprising in Eastern Jin Dynasty, Sun Enlu Xun's rebellion. Eleven years before and after rebellion, they moved into much of southeast, causing severe damage to economy of Eastern Jin dynasty. This uprising was also beginning of decline of nobility.

Lu Xun's rebellion also directly affected Liu Yu's Northern Expedition. In 409, Liu Yu led an army in Northern Expedition, and in second year he broke through city of Guanggu, captured its king Murong Chao alive, and Nanyang died. However, Liu Yu could no longer send troops to Hebei. As soon as Liu Yu destroyed Nanian, remnants of Sun En's forces, led by Lu Xun and Xu Daofu, rebelled in Jiaozhou. A large area is located near Jiankang. In such a critical situation, Liu Yu hurried back to courtyard with his teacher. In 411, Liu Yu defeated rebellious army of Lu Xun and temporarily stabilized situation in south. In case of sharp class conflicts, how could Eastern Jin Dynasty send main labor force on expedition?

Looking at entire history of Eastern Jin Dynasty for about 100 years, there is a general feeling of peace and tranquility. In fact, various contradictions are intertwined. Since Sima Rui went south, there have been wars in south such as Wang Dun's rebellion, Su Jun's rebellion, Zhou's rebellion, Huan Wen's dictatorship, Jin Huan Xuan's replacement, Liu Yu Huan's destruction, Rush Liu, Sun En and Lu Rebellion Xunya. It is said that wars were often fought in north at that time, and same was true in Eastern Jin Dynasty. How could such a dynasty unite world?