The Partition of Jin (simplified Chinese: 三家分晋; traditional Chinese: 三家分晉; pinyin: Sānjiā Fēn Jìn; lit. 'Three Families Partitioning Jin'), the watershed between the Spring and Autumn and Warring States periods, refers to the division of the State of Jin between rival families into the three states of Han, Zhao and Wei. As a result, the three states were often referred to as the "Three Jins" (三晋; 三晉; Sān Jìn).

Because the process took several decades, there is some debate between scholars as to the year which best marks the true partition of Jin. Kiser & Cai (2003) state the most common dates picked by historians are 481, 475, 468, and 403 BCE. The last date, according to Sima Guang marks the conferring of Marquessates by King Weilie of Zhou on Wei Si, ruler of the State of Wei; Zhao Ji, ruler of the State of Zhao, and Han Qian, ruler of the State of Han.^[1]

In 386 BCE, the states of Han, Wei and Zhao deposed Duke Jing of Jin and divided the last remaining Jin territory between themselves, which marked the end of the Jin state.

Succession issues were constant in Jin as far back as seventh century BCE. Even when, for example, King Xi of Zhou used his royal clout to give legitimacy to Wu of Quwo as the rightful duke of Jin in 678 BCE, succession issues continued to arise.^[2]

At the same time that the Jin duke was conquering new lands, a process of "subinfeudation" or "rear vassalage" occurred in the early and middle parts of the Spring and Autumn period, wherein aristocratic title and territory were awarded to vassals loyal to Jin, rather than to the Zhou royalty.^[3] However, Jin was unique among the major states in a major respect; whereas other states often enfeoffed the cadet branches of the ruling house, Jin had a policy of exiling or disempowering its own cadet houses. Instead, powerful ministerial families arose which were given fiefs like cadet houses in other states. For example, the house of Zhao descended from Zhao Cui, while the house of Wei descended from Wei Chou, both of whom were retainers of Duke Wen of Jin; the house of Han in turn descended from Han Wan, who was an uncle of Duke Wu of Jin.

Over time, while other powerful states (like Chu) were centralizing power through a rising bureaucracy, Jin continued to have a feudal power structure with aristocratic families ruling even individual counties.^[4] Over the course of a few generations, the major aristocratic families gained enough power to undermine the ruling duke's authority.^[5] During most of the seventh and sixth centuries BCE, Jin was composed of an assortment of semi-independent city-states fighting each other and the Jin Duke as much as they fought other states.^[6] In one extreme case, Viscount Xian of Xi, a retainer of Duke Jing of Jin, attempted to invade the state of Qi with only the troops under his command.^[7]

The House of Zhao (趙/赵) gained in prominence after Duke Wen placed them in charge of newly conquered lands^[8] such that, in 607 BCE, they deposed a duke that attempted to curb their political power.^[9] The Xian clan (先) was eliminated in 596 BCE.^[10] Duke Li of Jin encouraged the Luan clan (栾) to lead a military coalition that squashed the rising power of the Xi clan (郤). Subsequently, in 573, Luan supporters had Duke Li murdered and placed a puppet on the throne^[11] and the clan was then itself eliminated by 550, making the Zhi, Zhao, and Han (韩) clans the most powerful at about this time. Soon after, the Wei clan (魏) also grew in power.^[12]

In the leadup to the civil war, the dominant clans were the Zhao, Wei, Han, Fan (范), Zhi (智) and Zhonghang (中行) who were collectively called the "Six Titled Retainers" (Chinese: 六卿; pinyin: Lìu Qīng). These six aristocratic families dominated Jin in the late Spring and Autumn period, basically using the ruling duke as a figurehead until Jin was split into three separate states.^[13]

After the 546 BCE truce agreement between Jin and Chu (itself prompted in part by Jin's internal difficulties), conflicts between aristocrats and with the Duke escalated and a civil war (497–453 BCE) commenced.

In 514 BCE, Yangshe clan and Qi clan's force was destroyed by the conspiracy of Zhao, Han, Wei, Zhi, Zhonghang and Fan clan. During the time of Duke Ding of Jin (511–475), the Fan and Zhonghang clans were in turn eliminated, leaving only the Zhi, Zhao, Han, and Wei clans remaining. By about 450s BCE, the Zhi clan was the most dominant and began demanding territory from the other clans.

Duke Ai of Jin died in 434 BCE and was succeeded by Duke You of Jin. The Han, Zhao and Wei clans divided up surplus Jin territory amongst themselves, leaving only Jiang County and Quwo County (both in modern-day Shanxi Province) for Duke You of Jin.

Because Zhao Xiangzi was the younger son who forced his way to the inheritance, he decided to name his elder brother Zhao Bolu (simplified Chinese: 赵伯鲁; traditional Chinese: 趙伯魯) and his descendants as heir, with Bolu's grandson Zhao Xianzi (simplified Chinese: 赵献子; traditional Chinese: 趙獻子) eventually becoming heir apparent. However, after Zhao Xiangzi died, his son Zhao Huanzi (simplified Chinese: 赵桓子; traditional Chinese: 趙桓子) banished Zhao Xianzi and appointed himself ruler of the Zhao estates and paramount minister of Jin. Zhao Huanzi himself died a year later, whereupon the Zhao clan and vassals killed all of his sons and invited Zhao Xianzi back. Later on, Zhao Xianzi's son Marquess Lie of Zhao succeeded as ruler.

In 349 BCE, the Han and Zhao states divided the remaining Jin territory between themselves, thus marked the end of the state of State of Jin.