During the late Warring States period, following Fan Ju's strategy of "befriending distant states while attacking those nearby," the state of Qin first launched an attack on the state of Han, breaching Yewang in Han and besieging Shangdang. To make Qin withdraw its troops, the King of Han ordered the defending general Feng Ting to cede Shangdang to Qin. Unwilling to surrender to Qin, Feng Ting decided to offer Shangdang to the state of Zhao instead. The King of Zhao gladly accepted and sent General Lian Po to lead his army and station at Changping to prevent Qin forces from attacking.
The King of Qin, unwilling to accept that Shangdang had become part of the Zhao territory, sent Wang He to lead an army and attack Changping. The Qin forces repeatedly issued challenges, but the Zhao army, taking advantage of the terrain, held their positions and refused to engage. The war dragged on for three years, causing great suffering among the people. The people of Zhao had no grain to eat and asked Qi for food, but Qi stood by and did nothing; the Qin treasury was also drained by the war, and its soldiers grew weary. Both states could barely bear the burden of the conflict and hoped for a quick resolution.
After all, the State of Qin had strategists like Fan Ju; when the State of Zhao sent envoys to Qin to negotiate peace, they deliberately treated the envoys warmly, leading other states to mistakenly believe that Qin and Zhao had already reconciled, thereby depriving Zhao of the possibility of forming alliances with other states and leaving it isolated and helpless. At the same time, Qin sent people to Handan, the capital of Zhao, to bribe officials close to the King of Zhao, spreading rumors that Lian Po was avoiding battle because he intended to surrender to Qin, and that the person the Qin army truly feared was actually Zhao Kuo.
The state of Qin spread such rumors to pressure the King of Zhao into recalling Lian Po. Lian Po avoided battle because he knew the Qin army had traveled a long distance and sought a quick victory; he aimed to use the terrain's advantages to exhaust the Qin forces and counterattack only after their morale had waned. The King of Zhao, failing to understand this, repeatedly urged him to engage. Lian Po held his ground, refusing to fight for three months. The king finally grew suspicious, and Qin's scheme succeeded—Zhao indeed replaced Lian Po with Zhao Kuo to command the entire army.
After Zhao Kuo became the general, he completely reversed Lian Po's battle strategies, causing the morale of the Zhao army to waver. He also planned to launch an aggressive offensive, hoping to achieve a decisive victory and annihilate the Qin army. When news of Zhao Kuo's appointment reached the Qin state, the Qin immediately adjusted their battle tactics, dispatched additional troops, and replaced their general with Wu'an Jun Bai Qi. To avoid alerting the Zhao army and arousing their suspicion, the King of Qin ordered, "Anyone who dares to leak that Bai Qi is the general will be executed without mercy."
Bai Qi was a renowned general of the Qin State, rising from an ordinary military officer to the rank of Lord Wu'an. He commanded over seventy battles without a single defeat. Bai Qi's warfare was not merely about capturing cities; he relentlessly pursued and annihilated the enemy, aiming to wipe them out completely. By the late Warring States period, the name Lord Wu'an Bai Qi had become one that struck terror into the armies of the six other states.
Zhao Kuo lacked practical combat experience and was both overly eager for victory and careless toward his enemy, all weaknesses that were exploited by Bai Qi. In August of 260 BCE, Zhao Kuo, who knew almost nothing about the enemy's situation, led the main Zhao army in a massive assault on the Qin forces. Bai Qi feigned defeat after minimal resistance, luring Zhao's troops into pursuit. The Qin army retreated toward a pre-built fortified position, drawing the Zhao forces into their ambush site—Changbi. Bai Qi's encirclement was like a large sack; once all Zhao troops had entered, a 25,000-man force hidden on both sides of the encirclement immediately cut off their retreat from the rear, sealing the sack's opening while also monitoring the Zhao troops left behind at the rear camp, pinning them down so they could not come to reinforce. In this way, the main Zhao army was tightly trapped within the encirclement.
The Qin army cut off the Zhao army's retreat, leaving them without a source of food supplies, so they had to fight desperately within the encirclement while waiting for reinforcements. When news of the Qin army's siege reached the state of Qin, the King of Qin personally went to Henei and conscripted all men over the age of fifteen in the region, forming a force to assist in the battle at Changping. This force advanced north of Changping, blocking Zhao's grain routes and reinforcement channels, completely cutting off logistical support for the main Zhao army. By September of that year, the Zhao army had been without food for 46 days, with countless soldiers dying of starvation, and they had completely lost their will to fight.
Zhao Kuo hoped to break out of the encirclement, so he divided his army into four groups to launch successive attacks on the Qin camp, trying to carve a path to survival with sheer flesh and blood, but the Qin forces stood firm as fortresses. In the end, Zhao Kuo personally led his elite troops in a desperate attempt to force a breakthrough, only to be shot down by a volley of arrows from the Qin archers. With their commander killed, the Zhao army fell into chaos, and over 400,000 soldiers laid down their weapons and surrendered.
The surrender of over 400,000 Zhao soldiers troubled Bai Qi: their surrender to Qin was a last resort, made without food supplies or reinforcements. Their homeland was Zhao, so they would not truly be loyal to Qin, making this army unusable for Qin; if released, it would be like letting a tiger back into the mountains; guarding them all would require manpower, resources, and food that Qin could not afford; moreover, their large numbers made rebellion a serious risk if control was lost. After much deliberation, Bai Qi made a startling decision. He selected the youngest 240 Zhao soldiers, sent them back to Zhao to deliver the news, then led the rest into a valley and buried them alive.
This is the famous Battle of Changping in history, which severely crippled the Zhao state, leaving it unable to recover. More than half of Zhao's adult males died in this battle. The war terrified the other six states and accelerated Qin's unification of the entire country, making Qin's dominance over all under heaven almost inevitable.