During the Spring and Autumn period, the state of Qi, which had originally dominated the Central Plains, began to decline following the death of Duke Huan of Qi. Taking advantage of this opportunity, the southern state of Chu expanded its influence into the Yellow River basin. King Cheng of Chu thwarted Duke Xiang of Song's ambitions for hegemony at the Battle of Hongshui, greatly boosting Chu's military prestige. Subsequently, Chu gained control over numerous small and medium-sized states, including Zheng, Xu, Chen, Cai, Lu, Wei, Cao, and Song, extending its sphere of influence across the regions between the Yangtze, Huai, Yellow, and Han Rivers. Chu could be described as powerful and formidable in its strength and reputation.
Just as the state of Chu was rapidly expanding its power, the state of Jin also rose to prominence. In 636 BCE, Duke Wen of Jin, after enduring a long and arduous exile, finally returned to his state and ascended the throne. Upon taking power, he appointed capable officials such as Zhao Cui and Hu Yan, stabilizing Jin's political situation while developing the economy and strengthening the military, leading to growing national power. Alongside domestic reforms, he also championed the cause of "honoring the king" externally. When a usurpation and civil strife broke out in the Zhou royal court, King Xiang of Zhou fled to the state of Zheng and called upon the feudal lords for military assistance, but none were willing to send troops. By this time, Jin had gradually built up the strength to contend for hegemony over the Central Plains, and Duke Wen of Jin saw this as an opportunity to test his might. Thus, he quickly dispatched forces to help King Xiang of Zhou suppress the rebellion and escorted the king back to the capital. This move greatly enhanced Jin's prestige among the Central Plains states.
The rise of the Jin state alarmed Chu. King Cheng of Chu occupied the Gu region of Qi (present-day Dong'e, Shandong) and installed Prince Yong, threatening Qi's security. Jin, in turn, allied with Qi and Qin to confront Chu, escalating tensions between the two states. War between Jin and Chu was imminent, and when Song turned against Chu to side with Jin, the conflict fully erupted.
In the Battle of Hongshui, Duke Xiang of Song was defeated, struck by an arrow, and died shortly after, forcing the State of Song to submit to Chu. Later, Duke Xiang's son ascended the throne as Duke Cheng of Song. Years earlier, when Duke Wen of Jin was in exile and passed through Song, Duke Xiang had aided him, creating an old bond between Song and Jin. Seeing that Jin's power had grown after Duke Wen took the throne, Duke Cheng of Song decided to switch allegiance to Jin.
To maintain its dominant position in the Central Plains, the State of Chu launched an attack on the State of Song, thereby seeking to curb the expansion of Jin's influence. In the winter of 633 BC, Chu led a coalition of five states—Chen, Cai, Zheng, and Xu—to invade Song, besieging its capital, Shangqiu. In this crisis, Duke Cheng of Song sent Grand Minister Gongsun Gu to the State of Jin to request assistance.
Duke Wen of Jin consulted with his ministers. Xian Zhen, the commander of the Jin army, believed this was a perfect opportunity to "repay kindness, rescue the distressed, win prestige, and establish hegemony," and that they should seize it. Duke Wen of Jin had long harbored ambitions to dominate the Central Plains, so he wanted to use this chance to send troops there under the pretext of rescuing Song. However, he had once received favor from the King of Chu during his exile, and attacking Chu to save Song seemed morally questionable. At this point, Hu Yan proposed a plan: Chu had recently formed an alliance with Cao and married into Wei, both of which had previously shown disrespect to Duke Wen. Attacking Cao and Wei would be entirely justified, and Chu would surely send troops to aid these two states. This would lure the Chu army northward, lift the siege of Song, and avoid giving others grounds for criticism. Moreover, with the Chu army marching north in exhaustion, Jin could benefit from waiting at ease to meet the weary enemy.
With this strategic plan in place, Duke Wen of Jin solidified his resolve to dispatch troops. Subsequently, the ruler and ministers of Jin actively began preparations for war; Duke Wen reviewed the army, expanded the three armies, and appointed a group of capable officials as commanders of the various forces.
In early 632 BC, the state of Jin prepared for war, and Duke Wen of Jin mobilized his three armies and seven hundred chariots to cross the Yellow River, attacking the state of Wei. They captured Wulu in Wei and advanced eastward to take Lianyu (southeast of present-day Puyang, Henan). Meanwhile, he sent envoys to establish friendly relations with the state of Qi, successfully forming an alliance with Duke Xiao of Qi. With Qi and Jin allied, the Jin army marched to the capital of Wei. The Marquis of Wei sought peace with Jin, but Duke Wen refused. The Marquis then attempted to defect to Chu, but his people opposed this and expelled him, surrendering to the Jin army. Without a fight, Jin occupied Wei. In March, the Jin army moved south to attack Cao, capturing its capital Taoqiu (present-day Dingtao, Shandong) and taking Duke Gong of Cao prisoner.
Originally, the Jin army attacked Cao and Wei in order to lure the Chu forces north to rescue them, thereby lifting the siege on Song. However, despite Cao and Wei's urgent pleas for help, the Chu army remained unmoved and instead intensified their assault on Shangqiu. Song again sent an urgent plea to the Jin army.
Faced with this situation, Duke Wen of Jin found himself in a dilemma: if he did not march south to rescue Song, the state of Song, unable to withstand the pressure, would surely surrender to Chu and sever ties with Jin, leaving Jin in a passive position and harming his plans to dominate the Central Plains; if he did march south to rescue Song, the original strategy of luring the Chu army northward to fight a decisive battle in the territories of Cao and Wei could not be carried out. Moreover, Jin's military forces were limited, far from home, and there was no certainty of victory against the powerful Chu army. So Duke Wen of Jin summoned his ministers for discussion again. Xian Zhen, after analyzing the situation, proposed a plan: have Song outwardly distance itself from Jin, send envoys to bribe the states of Qi and Qin, and ask them to request that Chu withdraw its troops. Meanwhile, Jin would give part of the lands of Cao and Wei to Song to strengthen Song's resolve to resist Chu. Since Cao and Wei were originally allies of Chu, this move would surely anger Chu, causing it to reject the mediation of Qi and Qin. Qi and Qin, pleased by the bribes and angered by Chu's stubbornness, would then side with Jin if their persuasion failed, deciding to send troops to fight against Chu.
Duke Wen of Jin found this plan excellent and immediately began to implement it. When Chu failed to capture Shangqiu and the territories of Cao and Wei were given to Song, King Cheng of Chu indeed became furious and rejected the mediation efforts of Qi and Qin. At that time, Qi and Qin were both major powers, and seeing that Chu had shown them no respect, they too became greatly angered, abandoning their neutral stance to send troops in support of Jin. As a result, a strategic alliance of three great powers against Chu was formed, fundamentally reversing the balance of power between Jin and Chu.
King Cheng of Chu, seeing that the Jin army had defeated Cao and forced Wei to surrender, forming an alliance with Qi and Qin, realized that the situation in the Central Plains was clearly unfavorable to him. Fearing that Qin might take the opportunity to attack his rear, he proactively withdrew the Chu army to Shenyi (present-day Xingyang, Henan) in Chu territory and ordered Prime Minister Ziyu to lift the siege of Shangqiu, avoiding conflict with Jin. King Cheng told Ziyu that the Marquis of Jin, after nineteen years of exile, had finally gained control of Jin, enduring countless hardships and dangers along the way—he was no ordinary man, and his virtue made him invincible. He advised Ziyu to act within his means and retreat when faced with difficulties. However, Ziyu, arrogant and overconfident, ignored King Cheng's advice and insisted on fighting Jin, requesting additional troops. King Cheng hesitated, unwilling to engage in battle with Jin yet hoping Ziyu might achieve a lucky victory. Although he granted Ziyu's request for a decisive battle, he only sent 600 royal guards as reinforcements.
After his request to fight was approved and he received reinforcements from King Cheng of Chu, Ziyu became even more determined to engage the Jin army in battle.
To find a pretext for a decisive battle, Ziyu sent an envoy, Wan Chun, to negotiate with Jin, proposing a "truce" condition: if the Jin army restored the states of Cao and Wei, the Chu army would withdraw from Song. This was actually Ziyu's strategy to kill three birds with one stone. According to his plan, if Jin accepted the truce terms, then Cao, Wei, and Song would all be grateful to Chu; if Jin refused, then Jin would incur the resentment of Cao, Wei, and Song. Either way, Jin's efforts to dominate the Central Plains and command the other states would be in vain.
Xian Zhen saw through Ziyu's intentions and devised an even cleverer counter-strategy, having the state of Jin secretly negotiate with Cao and Wei, promising to restore their states on the condition that they break ties with Chu, while also detaining Chu's envoy Wan Chun to provoke Ziyu into seeking battle. Cao and Wei betrayed Chu and defected to Jin, and with their envoy held by Jin, the arrogant Ziyu, enraged and humiliated, relied on the numerical superiority of the combined Chu, Chen, and Cai forces to aggressively march toward Taoqiu, seeking a decisive battle with the Jin army.
Originally, when Duke Wen of Jin, then a prince, sought refuge in the State of Chu, he promised King Cheng of Chu that if the two states ever clashed in the Central Plains, the Jin army would retreat three days' marches to repay Chu's great kindness. Now, as the armies of Jin and Chu indeed met, Duke Wen honored his word by ordering the Jin forces to withdraw three stages from the Chu capital of Taoqiu and encamp at Chengpu (south of present-day Fan County, Shandong). Troops from Qi, Qin, and Song also arrived at Chengpu to join the Jin army. On the surface, Duke Wen's retreat was a gesture of gratitude to King Cheng, but in reality, it aimed to avoid the Chu army's initial momentum, lure the enemy deeper, exhaust their forces, and gather allied troops from Qi and Qin to choose a favorable moment for a decisive counterstrike.
The Jin army's voluntary retreat aroused suspicion among many in the Chu forces, who advocated halting the pursuit and adopting a wait-and-see attitude. However, the stubborn and self-opinionated Ziyu believed that the Jin army's withdrawal presented a perfect opportunity to pursue them and recapture Cao and Wei, so he led his troops in a rapid advance, following the Jin army all the way to Chengpu.
In April 632 BCE, the armies of Jin and Chu engaged in a major chariot battle at Chengpu. Ziyu divided the Chu forces into three divisions: center, left, and right. The elite main force formed the center, which he commanded directly; the Chen and Cai troops, attached to the Chu right wing, were led by Chu general Zixi; the Zheng and Xu troops, attached to the Chu left wing, were commanded by Zishang.
The Jin army's three-army formation: Xian Zhen as commander-in-chief leading the central army; Hu Mao leading the upper army with Xi Zhen and Hu Yan as deputies; Luan Zhi leading the lower army with Xu Chen as deputy.
The Jin army analyzed the Chu army's situation, concluding that while the Chu central forces were strong, their left and right flanks were weak in combat capability; moreover, the Chu commander Ziyu was arrogant and underestimated the enemy, lacking knowledge of the Jin army's true strength, so they decided to act with clear purpose—first attacking the two flanks, then launching an assault on the central army.
The Jin commander Xian Zhen ordered an initial attack on the weaker right flank of the Chu army, which consisted of troops from the Chen and Cai states. Jin's lower army deputy commander Xu Chen was ordered to meet the enemy, whose forces had many warhorses and charged fiercely. Xu Chen covered his chariot horses with tiger skins and charged into the enemy formation. The horses and soldiers of Chen and Cai, not knowing the truth, thought real tigers were charging at them, panicked instantly, and fled in disorder. The right wing of Chu was immediately routed.
Chu generals Ziyu and Zishang, seeing their right wing routed, flew into a rage and launched a fierce assault on the Jin central and upper armies. The Jin army then employed a strategy of luring the enemy out and then splitting and annihilating them to counter the Chu left wing's fierce attack. The Jin upper army feigned a retreat, with its commander Humao deliberately placing the two large banners of the commander and deputy commander on his chariot before pulling back. To make the Chu forces believe the rear had withdrawn, Luan Zhi, commander of the Jin lower army, also had his troops drag tree branches behind their chariots at the rear of the formation, raising clouds of dust. Chu general Ziyu, failing to see through the Jin ruse, genuinely believed the Jin right wing was retreating and blindly ordered the Chu left wing to pursue, thereby exposing its flank. Jin generals Xian Zhen and Xi Zhen then led the central army to strike the Chu left wing from the side, while Jin upper army commander Humao and his deputy Huyan seized the opportunity to turn back and attack from the other side. The Chu left wing, now completely surrounded with no escape route, was soon routed by the Jin forces as well.
Seeing that both the left and right flanks had been defeated and the overall situation was lost, Ziyu ordered the central army to cease its attack and quickly withdraw from the battlefield, which allowed the central forces to be preserved. After the Chu army's defeat, they retreated to Liangu (in present-day Xihua, Henan), where Ziyu was reprimanded by King Cheng of Chu and, overwhelmed with shame and anger, committed suicide.
The Battle of Chengpu ended with a decisive victory for the Jin army, which thwarted Chu's northward expansion and forced it to retreat south of the Tongbai and Dabie Mountains, stabilizing the Central Plains. After the battle, the Jin army entered Hengyong in Zheng and built a temporary palace for the Zhou king at Jiantu near Hengyong, presenting captives to him. The Zhou king personally went to Jiantu to reward the Jin army and granted Duke Wen of Jin the title of "Marquis-Earl." Duke Wen of Jin then convened a meeting at Jiantu with the rulers of seven states, including Qi, Lu, Song, and Wei, where they pledged allegiance to the Zhou king, establishing Jin as the hegemon of the Central Plains.
The Battle of Chengpu was the first major strategic showdown between the states of Jin and Chu as they vied for supremacy over the Central Plains. In this conflict, the states of Qi and Qin merely voiced support for Jin without actually participating in the fighting, so in terms of military strength, Chu held the advantage. However, Jin pioneered the concept of "all is fair in war," winning through strategy and adopting a correct approach in battle command by leveraging their strengths, avoiding weaknesses, and striking after the enemy had exhausted themselves, ultimately defeating Chu and securing dominance over the Central Plains.