The ancient Jin Dynasty covered two separate periods - the Western Jin (265-316) and the Eastern Jin (317-420). The Western Dynasty was established by Sima Yan (also known as Emperor Wu) in Luoyang and the Eastern Dynasty was founded by Sima Rui in Jiankang ( Nanjing today).
Prior to the formation of the Jin Dynasty, Sima Yi was a Minister of the Wei State (220-265). He was a brilliant military tactician during the wars against the Shu State (221-263) and the Wu State (220-280).In 239, Wei State Emperor Mingdi died and Sima Yi and Cao Shuang were named as co-leaders of the state's military forces. From the beginning, the two men engaged in a fierce power struggle. Initially Cao grasped the real power, but Sima Yi would ultimately prevail. Once when Cao and the Wei Emperor traveled to sweep Mingdi's tomb, Sima Yi took over Cao Shuang's compound, his arsenals and blocked access to the city of Luoyang. He then forced the Empress to abolish the official positions of Cao Shuang and his brother. At this point Sima Yi asked the Emperor to remove Cao Shuang and his brother from power. Seeing no alternative Cao resigned. Shortly after, however, Cao and many of his colleagues were executed for treason. This put Sima Yi into position to begin his autocratic rule of the Wei State.
After Sima Yi's death, his family's forces in the Wei State were gradually consolidated by his sons Sima Shi and Sima Zhao. The sons didn't get along and fought several skirmishes against each other. In 263, Sima Zhao hatched a plan to claim the throne for himself. He ordered his generals Zhong Hui and Deng Ai to attack the Shu State. When the army of the Wei State marched on Chengdu, Shu's capital city, its King Liu Shan surrendered in despair. This effectively drove the Shu State out of existence. Later, Zhong Hui befriended Jiang Wei, a former Shu general. They plotted a revolt, but were suppressed by Sima Zhao. Soon after, Sima Zhao died and his son Sima Yan usurped the throne of the Wei State in 265. This marked the establishment of the Jin Dynasty. Sima Yan named himself Emperor Wu and made Luoyang the capital of his empire.
After ascending to the throne, Sima Yan was able to unify China for a short period of time. However, he couldn't deal with the omnipresent social problems that poisoned the political atmosphere. Gradually the situation deteriorated to the point where the imperial court was in a total state of disarray. Several factions began to contend for power. The noted 'Eight-King Rebellion' was launched by the eight kings Sima Yan had previously named. This scramble for ruling power over the Jin Dynasty left the empire badly weakened. Nomadic tribes living to the north were constantly on the attack and seiaed the opportunity to establish their own regimes. The Huns, Di, Jie, Xianbei and Qiang Peoples successively founded a series of states historically called 'The Sixteen Kingdoms of the Five Barbarian Peoples.' By the year 317, the Jin Dynasty had lost its sovereignty.
In 317, the imperial family and remnants of the Jin court fled to the south. Sima Rui proclaimed himself emperor in Jiankang and re-established the Jin Dynasty. Autocratic rulers and military crises plagued the Eastern Jin Empire throughout its 104 years' existence. Rebellions were frequent as different individuals attempted to claim the throne. During this time Sima Rui died in sorrow and indignation. Emperor Gong was the last ruler of the Eastern Jin Dynasty and he lasted for only one year after being dethroned by General Liu Yu. This event marked the end of the Eastern Jin Dynasty and the beginning of the Liu Song and Southern Dynasties.