After Han Xin pledged allegiance to Liu Bang, he was appointed as a general and quickly demonstrated his exceptional military talent. Leading his army eastward, he swiftly conquered the states of Wei and Dai, then marched through the Jingxing Pass to attack Zhao.
When King Zhao heard the news, he personally led his general Chen Yu and an army of 200,000 to defend against the Han forces at Jingxing Pass. The Zhao strategist Li Zuoche proposed to Chen Yu, 'Give me 30,000 men, and I will use the rugged terrain to ambush the Han army's supply lines and cut off their retreat.' But Chen Yu, overconfident in his own strength, dismissed the plan and refused to adopt Li Zuoche's strategy.
Han Xin, delighted by the situation, led his army to camp thirty li from the Jingxing Pass. At midnight, he selected two thousand elite soldiers, each carrying a red Han army banner, and ordered them to ambush in the woods near the Zhao camp. "When battle begins at dawn," Han Xin instructed, "seize the chance to storm their camp, tear down their flags, and plant our red banners in their place."
At dawn the next day, Han Xin deliberately arrayed his troops with their backs to the river, baiting the Zhao army to attack. As the two forces clashed, Han Xin ordered his men to abandon their banners and drums and retreat toward the water. The Zhao commander, unaware this was a feigned retreat, committed his entire army to the pursuit, with soldiers scrambling to seize the discarded Han equipment.
The two thousand soldiers hidden near the Zhao camp, seeing the Zhao army pour out entirely, immediately stormed into the Zhao camp, tore down all their flags, and replaced them with Han red banners. When the Zhao troops saw this, they believed their king had been captured by the Han army, panicked in confusion, and lost all will to fight.
Han Xin immediately led his forces in a counterattack, crushing the Zhao army in a decisive defeat.
Later, the idiom "Changing Banners" came to be used as a metaphor for using strategy to replace someone or something.
Source: *Records of the Grand Historian*, "Biography of the Marquis of Huaiyin"
Meaning of the Idiom: Later, the Chinese idiom "拔帜易帜" came to describe using strategy to replace someone or something.