In 379 BCE, Duke Kang of Qi died, and the Jiang clan's rule over the state of Qi was replaced by the Tian family, after which the state became known as "Tian Qi." Jiang Ziya had rendered outstanding service in helping establish the Zhou Dynasty, and King Wu of Zhou enfeoffed him with the state of Qi, which was already a formidable power at the time. After decades of development, by the time of Duke Huan of Qi, Jiang Xiaobai, Qi had become one of the leading great powers. However, even Jiang Taigong likely never imagined that his fief would eventually slip from the hands of his descendants, with the Tian family becoming its new masters.
Chen Wan was the son of Duke Li of the State of Chen. After his birth, Duke Li cast a divination for him, and the oracle said that Chen Wan's descendants would become emperors, but not in the State of Chen. Duke Li was half-convinced and half-doubtful. Sure enough, after Duke Li died, Chen Wan left the State of Chen.
In 672 BCE, Chen Wan arrived alone in the State of Qi. Duke Huan of Qi wanted to appoint him as a high minister, but Chen Wan declined, saying, "I am merely a fugitive seeking refuge; it is already more than enough that you do not kill me, and I dare not accept such a high position." So Duke Huan made him the Director of Works. Soon after, a high official wanted to marry his daughter to Chen Wan. For this, Chen Wan specifically performed a divination, which indicated that if the official's daughter married him, her sixth-generation descendant would become a high-ranking official, and the ninth-generation descendant would become a ruler. Thus, the official married his daughter to Chen Wan.
After Chen Wan's death, his descendants continued to serve as officials in the State of Qi. Five generations later, his descendant Tian Huanzi, also known as Wuyu, gained the favor of Duke Zhuang of Qi. After Tian Wuyu's death, his son Tian Qi served as an official under Duke Jing of Qi. This Duke Jing of Qi was a decadent ruler who spent his days indulging in pleasure, completely disregarding the suffering of the people. In his later years, he became even more dissolute and greedy for enjoyment. Even when the grain in the state treasury grew moldy, he refused to distribute it to disaster victims. Furthermore, he conscripted many commoners to build palaces for him, and ordered the amputation of hands and feet for those who resisted, causing widespread resentment among the people. Seizing this opportunity, Tian Qi devised a plan to win popular support. He changed the Qi state's measurement system from a base-four to a base-five system: when the people borrowed grain, he used the base-five system, but when they repaid, he used the base-four system. By lending out grain with a larger measure and collecting repayment with a smaller one, the people benefited greatly. They were all grateful to Tian Qi. Soon, the Tian family grew powerful and influential.
Once, Duke Jing of Qi sent Yan Ying as an envoy to the state of Jin, and Yan Ying privately said to Shu Xiang, "Qi will eventually belong to the Tian family." A few years later, while Yan Ying was resting with Duke Jing of Qi, the duke looked at his luxurious palace and sighed, saying, "After I die, who will live here?" Yan Ying replied, "If it is as you say, I am afraid it will only be the Tian family. Although the Tian family has not performed great deeds, they have shown kindness to the people. Your Majesty levies heavy taxes, but Tian Qi gives generously, so the people's hearts are all with him! If your descendants are even slightly negligent, the Tian family will seize control of Qi." Upon hearing this, Duke Jing of Qi was very worried. He sought advice from Yan Ying, who told him to govern with ritual propriety. Although the duke agreed, it was too late, and he died a few years later. In the end, he only managed to curb the Tian family's power but did nothing to win the people's hearts.
After Duke Jing of Qi fell gravely ill, he appointed Guo Xia and Gao Zhang as chancellors to assist his son Tu, who was made crown prince. Tian Qi was displeased upon learning this, as he wanted another son of Duke Jing, Yangsheng, to be the crown prince. After Duke Jing's death, Tian Qi pretended to support the two chancellors, Gao and Guo, while secretly sowing discord. He said to them, "Initially, most of the high officials did not want Tu to be crown prince. Now that you two have helped him ascend the throne, the officials are planning a rebellion!" Then he told the officials, "The chancellors are formidable and intend to eliminate those of us who opposed the prince's succession. Before they act, let us strike first!" Thus, Tian Qi led the officials and their troops into the palace. The chancellors Gao and Guo hastily fought back but ultimately were defeated.
Subsequently, Tian Qi brought Yang Sheng, who had fled to the State of Lu, back to his own home. He then summoned the high officials to his house for a banquet. Before this, he had hidden Yang Sheng in a sack, and midway through the gathering, he opened the sack, letting Yang Sheng out, and said, "This is the true ruler of the State of Qi." The officials knelt and paid homage. At that moment, one minister said, "Have you all forgotten the late Duke Jing's final decree?" The officials showed some signs of regret, so Yang Sheng kowtowed and said, "If you find me worthy, establish me as ruler; if not, then let it be." Faced with this situation, the officials had no choice but to agree. Yang Sheng is historically known as Duke Dao of Qi. After his accession, Tian Qi became the prime minister and monopolized all power in the State of Qi.
After Tian Qi died, Duke Dao of Qi was killed, and his son ascended the throne, becoming Duke Jian of Qi. At that time, Tian Chang served as the Left Prime Minister of Qi, while Jian Zhi served as the Right Prime Minister. Duke Jian of Qi favored Jian Zhi, which made Tian Chang jealous. Therefore, Tian Chang continued his father Tian Qi's old method: lending out grain with a larger measure and collecting it back with a smaller one. When the high officials of Qi went to court to advise Duke Jian to remove Tian Chang from his position, the duke did not take it seriously. Soon, the people of Qi all rallied to the Tian family. Around this time, a relative of Jian Zhi named Zi Wo told a distant relative of the Tian family that he intended to destroy the Tian clan. Unexpectedly, this Tian relative secretly reported Zi Wo's words to Tian Chang, saying, "Zi Wo is about to annihilate the Tian family. If you do not strike first, disaster will befall you." Upon receiving this news, Tian Chang led his men into the palace to kill Zi Wo. Duke Jian of Qi was about to order Tian Chang's arrest, but one of his attendants said, "Tian Chang is not rebelling; he is protecting the ruler's safety." So Duke Jian did not issue the order to arrest Tian Chang. However, when Tian Chang heard that Duke Jian was angry, he feared the duke would kill him, so he directly led his troops to kill Duke Jian. As a result, Duke Jian fled, and Jian Zhi was killed. Four years later, Duke Jian of Qi was assassinated by men sent by Tian Chang. Subsequently, Tian Chang installed Duke Jian's younger brother on the throne, while he himself assumed the position of Prime Minister. Through two armed struggles, the Tian family seized control of Qi and simultaneously weakened the power of the Jiang clan's great families, further diminishing the Jiang clan's influence.
After Tian Chang's death, 69 years passed during which two generations of the Tian family served as prime ministers for two reigns. By the time of Duke Kang of Qi, Tian He was the prime minister of Qi. Duke Kang of Qi indulged in wine and women, neglecting state affairs, so Tian He exiled him to a coastal city. Soon after, Tian He requested that the Zhou king appoint him as a feudal lord, and the Zhou king granted his request. In 386 BCE, Tian He became the Marquis of Qi, and from then on, the Jiang clan's rule over Qi was completely replaced by the Tian clan.