Usurpation of Qi by Tian
The Usurpation of Qi by Tian (Traditional Chinese: 田氏代齊), was the deposition of the Jiang clan (姜氏) as rulers of the state of Qi, and their replacement by members of the Tian clan (田氏). This occurred as a series of events between 481 and 379 BCE, through which the Tian clan cemented its position as the leading family in Qi. The final acts of this usurpation (391-379 BCE), in conjunction with the Partition of Jin (376 BCE), mark the transition from the Spring and Autumn Period to the Warring States period.
The Tian clan continued to use the name "Qi" for their realm after the usurpation. For historiographical purposes, pre-usurpation Qi is referred to as "Jiang Qi" (姜齊), while post-usurpation Qi is referred to as "Tian Qi" (田齊).
Qi was originally ruled by the Jiang clan, the descendants of Jiang Ziya. In 672 BCE, Prince Yuan of Chen fled to Qi following political unrest in his native fiefdom and adopted the surname of Tian, thus being the progenitor of the Tian clan. By 545 BCE, the Tian clan was one of the strongest families in Qi. Tian Huanzi, in conjunction with other prominent families, eliminated the Qing clan (慶氏), the Luan clan (欒氏), and the Gao clan (高氏).
At the same time, the Tian clan also sought the support of the minor Qi aristocrats and the Qi populace. Tian Huanzi granted fiefdoms to those Qi aristocrats who were not granted lands, and took steps to demonstrate his charity by providing food relief to the poor. His successor, Tian Xizi, garnered additional support through providing low-interest loans to the peasants. At the same time, the Dukes of Qi were seen as venal and corrupt; support for the Tian clan thus gradually overshadowed support for the Jiang clan.
In 489 BCE, Duke Jing of Qi died. The major cadet branches of the Jiang clan, the Guo clan (國氏) and the Gao clan (高氏, probably no relation to the earlier Gao clan), favored the accession of Prince Tu (公子荼) to the throne. On the other hand, Tian Xizi supported Prince Yangsheng, expelled the Guo and Gao clans, and then installed Prince Yangsheng on the throne as Duke Dao of Qi, with Tian Xizi himself as Prime Minister. After this, the Tian clan's status was paramount in Qi.
In 481 BCE, Tian Xizi's successor Tian Chengzi killed Duke Jian of Qi (and possibly his father Duke Dao of Qi as well in 485 BCE), as well as numerous members of the Jiang clan. He then installed Duke Jian's brother, Duke Ping of Qi to the throne. Following this, the Tian clan became the de facto rulers of Qi.
In 386 BCE, Tian He exiled the former Duke Kang onto a small island in the Yellow River delta and declared himself Duke. In the same year, the Zhou court formally recognized Tian He's new position as Duke, and legitimized the rule of the Tian clan over Qi.
In 379 BCE, the former Duke Kang died, thus ending a line that stretched back to the beginning of the Zhou Dynasty. The Tian clan's hold on Qi would continue until Qi's annexation by the Qin in 221 BCE.