In 262 BC, King Zhaoxiang of Qin dispatched the general Bai Qi to attack the state of Han, capturing the city of Yewang (present-day Qinyang, Henan). This cut off the connection between Shangdang Commandery (its seat located in present-day Changzhi, Shanxi) and the Han capital, placing Shangdang in a critical situation. The Han military leaders in Shangdang refused to surrender to Qin and sent an envoy to present the maps of Shangdang to the state of Zhao.
King Xiaocheng of Zhao (son of King Huiwen of Zhao) sent troops to take control of Shangdang. Two years later, Qin dispatched Wang He (pronounced "he") to besiege Shangdang.
When King Xiaocheng of Zhao heard the news, he quickly sent Lian Po with over two hundred thousand troops to relieve Shangdang. By the time they arrived at Changping (northwest of present-day Gaoping County, Shanxi), Shangdang had already fallen to the Qin army.
Wang He then turned his attention toward Changping. Lian Po immediately established a defensive position, ordering his soldiers to build fortifications and dig deep trenches to confront the advancing Qin forces, preparing for a protracted resistance.
Wang He repeatedly challenged the Zhao army to battle, but Lian Po refused to engage under any circumstances. Unable to devise a strategy, Wang He had no choice but to send word back to King Zhaoxiang of Qin: "Lian Po is an experienced old general who won't easily come out to fight. Our troops have traveled a long way here; if this drags on, we fear our grain supplies will run out. What should we do?"
King Zhaoxiang consulted Fan Ju for advice. Fan Ju said: "To defeat Zhao, we must first get Zhao to recall Lian Po."
King Zhaoxiang asked, "How can that be achieved?"
Fan Ju replied, "Leave it to me."
A few days later, King Xiaocheng of Zhao heard widespread discussion among his courtiers: "The Qin state is only afraid of the young and capable Zhao Kuo leading the army. Lian Po is useless and seems about to surrender soon!"
The Zhao Kuo mentioned was the son of Zhao She, a renowned general of Zhao. As a youth, Zhao Kuo loved studying military tactics. When discussing the principles of warfare, he spoke with great fluency and confidence, believing himself invincible, even looking down on his own father.
King Zhao believed the courtiers' chatter. He immediately summoned Zhao Kuo and asked whether he could repel the Qin army. Zhao Kuo replied, "If Qin sent Bai Qi, I would need to carefully consider how to counter him. But now they've sent Wang He, who is merely a match for Lian Po. If I were in command, defeating him would be effortless."
Pleased by this response, King Zhao appointed Zhao Kuo as the new general to replace Lian Po.
Lin Xiangru warned the king: "Zhao Kuo only knows how to recite his father's military manuals; he lacks the ability to adapt to battlefield situations. He must not be made commander." However, King Zhao ignored Lin Xiangru's advice.
Zhao Kuo's mother also submitted a memorial to King Zhao, begging him not to send her son. The king summoned her and asked for her reasons. She said: "When my husband was on his deathbed, he earnestly instructed me: 'Zhao Kuo treats warfare like a child's game. When he talks about military strategy, he is arrogant and looks down on everyone. It would be best if the king never employs him. If he is made a general, our Zhao army will surely be destroyed by him.' Therefore, I beg Your Majesty not to appoint him as general."
The king replied, "My decision is made. Please do not interfere."
In 260 BC, Zhao Kuo led two hundred thousand troops to Changping and received the military insignia from Lian Po. Lian Po handed over command and returned to Handan.
Zhao Kuo now commanded an army of four hundred thousand, a force of immense scale. He abolished all the regulations established by Lian Po and issued a new order: "Whenever Qin attacks again, we must counterattack head-on. Once the enemy is defeated, we must pursue them relentlessly until not a single soldier or piece of armor remains."
Meanwhile, Fan Ju received news that Zhao Kuo had replaced Lian Po. Knowing his scheme of sowing discord had succeeded, he secretly appointed Bai Qi as Supreme General to command the Qin forces. As soon as Bai Qi arrived at Changping, he set up ambushes and deliberately suffered several defeats. Unaware of the trap, Zhao Kuo pursued vigorously. Bai Qi lured the Zhao army into a pre-arranged ambush zone, then dispatched twenty-five thousand elite troops to cut off the Zhao army's retreat, and another five thousand cavalry to charge straight into the Zhao main camp, splitting the four hundred thousand Zhao soldiers into two isolated groups. Only then did Zhao Kuo realize the Qin army's true strength. He could do nothing but build defensive fortifications and hold out, awaiting reinforcements. Meanwhile, Qin sent additional troops to cut off all routes for Zhao reinforcements and supply convoys.
Trapped, Zhao's army ran out of food and water, with no hope of rescue. After more than forty days, the soldiers were miserable and had lost all will to fight. Zhao Kuo led his troops in a desperate attempt to break through the encirclement, but the Qin forces unleashed a hail of arrows, killing Zhao Kuo. When the Zhao army learned their commander had been slain, they threw down their weapons and surrendered en masse. The entire four hundred thousand strong Zhao army was annihilated—destroyed by their commander, Zhao Kuo, who had only ever talked about war on paper.