In the later years of the Wei, Sima family held the power court. After vanquishing the Shu, the Wei's strength dramatically increased. In 265, Sima Yan dethroned the Wei emperor and established the Jin Dynasty, known as Western Jin Dynasty. Capital was in Luo Yang. In 280, the Western Jin defeated the Wu and united the long-divided country. The succeeding years were relatively peaceful and stable ones, but this period was not long.
The Western Jin Dynasty was a state mainly composed of privileged landlords. Most political and economic measures instituted by Emperor Jin Wudi (Sima Yan) were meant to protect the benefits of these few. He conferred titles on more than 20 relatives in the Sima family in the hope of building up the influence of the royal family. The Western Jin government allowed officials of different ranks to possess fields, tenants and dependent families. The privilege of the officials and landlords was acknowledged. Most officials of court were held by officials from powerful or privileged families. This system ultimately became a tool for those families to expand their own power. The increasing strength of the powerful families and landlords during this period intensified the conflict between the officials and the commoners.
In 291, the wars for throne among the eight princes lasted about 16 years dislocated the social economy and shook the rule of the Western Jin. Emperor' power was weakened.
Ever since the Eastern Han Dynasty, ethnic minorities, who were Xiongnu, Xianbei, Jie, Di, Qiang in northwestern and northern areas kept migrating inland, which complicated the relations among different nationalities in north China. In the late Western Jin, these northern minorities were at odds with each other. They successively established their own governments in which the noble marshals would take the supreme position. In 308, Liu Yuan, a Xiongnu noble, made himself King of Han, and soon declared him emperor. After his death, his son Liu Cong sent troops to conquer the Western Jin capital Luoyang and captured Emperor Huai. Now the Western Jin existed in name only. Because this incident took place in the 5th year of Yongjia (311) of Emperor Huai, it was known as "the Yongjia Disturbance". During the disturbance, the northern people flocked to the south to escape the war, so this incident is also called "the Southward Transplant of Yongjia". In 316, the Xiongnu army entered Chang'an, captured Emperor Min of Jin and ended the Western Jin Dynasty.
The Western Jin Dynasty lasted 51 years, it was short, but it was the unified government during the period between the Wei, the Jin and the Southern and Northern Dynasties