Although the state of Qi had suffered a defeat at Changshao, it did not affect Duke Huan of Qi's later status as a hegemon. Over ten years later, the northern state of Yan (its capital in present-day Beijing) sent an envoy to request military aid, reporting that their state had been invaded and defeated by the Shanrong tribe nearby. Duke Huan decided to lead a large army to rescue Yan.
In 663 BC, when Qi's army arrived in Yan, the Shanrong had already looted people and treasures and retreated.
The armies of Qi and Yan joined forces and pursued northward. Unexpectedly, the enemy lured them into a labyrinthine valley. This maze-like valley was like an endless sea, with no borders or edges, making it impossible to find the original path.
It was Guan Zhong who came up with an idea. He said to Duke Huan: "Perhaps horses can recognize the way. Why not find several local old horses to lead the way? Maybe they can guide us out of this place."
Duke Huan ordered men to select several old horses to lead. Sure enough, these veteran horses successfully guided the troops out of the maze.
After helping Yan defeat the Shanrong, the state of Xing was invaded by another tribe, the Di. Duke Huan again led his forces to drive away the Di and helped Xing rebuild its city walls. Then, the Di attacked the state of Wei, and Duke Huan assisted Wei in rebuilding its capital on the southern bank of the Yellow River. Because of these deeds, Duke Huan's prestige greatly increased. Only the southern state of Chu (its capital near modern-day Jiangling, Hubei) refused to submit to Qi, standing in opposition and challenging Qi's supremacy.
Chu, located in southern China, had traditionally kept no contact with the central plains states. At that time, the feudal lords of the central plains regarded Chu as "barbarians." However, the Chu people cultivated the southern lands, gradually subdued neighboring tribes, and slowly grew into a powerful state. Later, they even declared their ruler as King of Chu, disregarding the Son of Heaven of the Zhou dynasty.
In 656 BC, Duke Huan assembled the armies of seven states—Song, Lu, Chen, Wei, Zheng, Cao, and Xu—and launched a joint attack on Chu.
King Cheng of Chu, upon hearing the news, also gathered troops to prepare resistance. He sent an envoy to meet Duke Huan, saying: "Our king has sent me to ask: Qi is in the north, Chu in the south; our states have long had no relations—truly, 'winds from the north may stir cattle in the south, but they are unrelated.' Why have your troops come here?"
Guan Zhong rebuked: "Although our states are far apart, both were enfeoffed by the Son of Heaven. When Qi's founding Duke Taigong received his title, he was given a mandate: whoever disobeys the Son of Heaven, Qi has the right to punish. Chu used to send annual tribute of bao-mao (a kind of reed used for filtering wine) to the Son of Heaven. Why has this tribute stopped now?"
The envoy replied: "Failing to send the bao-mao tribute was our fault. We will certainly resume it in the future."
After the envoy left, the allied forces of Qi and the feudal lords broke camp and advanced further, reaching Shaoling (in present-day Yan-cheng County, Henan; "Zhao" pronounced shào).
King Cheng of Chu then sent Qu Wan to inquire. To display his military might, Duke Huan invited Qu Wan to ride with him and inspect the arrayed troops of the central plains. Qu Wan saw indeed that the army was orderly, strong, and well-equipped.
Proudly, Duke Huan said to Qu Wan: "Look at this mighty force! Who could possibly resist it?"
Qu Wan smiled faintly and replied: "When a lord assists the Son of Heaven, upholds righteousness, and aids the weak, others respect him. But if one relies solely on military power, though our state may not be strong, we have Fangcheng Mountain (the Great Wall built by Chu, stretching from present-day Fangcheng, Henan, northeast to Biyang) as our wall and the Han River as our moat. Even if you bring more troops, it's uncertain whether you could break through."
Hearing Qu Wan's firm response, Duke Huan estimated that defeating Chu would not be easy. Moreover, since Chu had admitted fault and promised to resume tribute of bao-mao, Qi had saved face. Thus, the eight feudal states of the central plains and Chu concluded an alliance at Shaoling before returning home.
Later, a dispute arose within the Zhou royal family. Duke Huan again helped Crown Prince Ji Zheng consolidate his position. After the prince ascended the throne as King Xiang of Zhou, the king sent a special envoy to present Duke Huan with sacrificial meat from the ancestral temple—a great honor.
Seizing this opportunity, Duke Huan convened the feudal lords again at Kuiqiu in the state of Song (east of present-day Lankao, Henan), hosted the royal envoy, and established a new covenant. Its main provisions were: build water conservancy projects and prevent floods; do not use neighboring states as reservoirs; do not prohibit grain sales to neighbors during famines; and all allied lords must treat each other amicably after forming the alliance.
This was Duke Huan's final gathering of the feudal lords. Such large-scale alliances occurred many times; historically, they are known as the "Nine Alliances with the Feudal Lords."
In 645 BC, Guan Zhong died. Two years later, Duke Huan himself passed away. Upon Duke Huan's death, his five sons fought for the throne, causing internal chaos in Qi. Prince Zhao fled to the state of Song. Thus ended Qi's status as the dominant power.