The idiom "Pulling Down Flags and Raising New Ones" (Bá Zhì Yì Zhì) means to replace one thing with another, or to supplant something entirely.
This idiom originates from the "Biography of the Marquis of Huaiyin" in *Records of the Grand Historian (Shiji)*: "At midnight, troops were dispatched. Two thousand light cavalry were selected, each carrying a red flag, taking a secret mountain path to observe the Zhao army. They were instructed: 'When Zhao sees us flee, they will surely empty their camp to pursue us. Quickly enter the Zhao camp, pull down the Zhao flags, and raise the Han red flags.'"
After Han Xin was appointed as the great general by Liu Bang, he led the Han army to conquer the states of Wei and Dai. Then, with the assistance of Zhang Er, he led several tens of thousands of troops eastward down Jingxing Pass to attack the state of Zhao. The King of Zhao and his commander Chen Yu gathered an army of two hundred thousand at Jingxing Pass to block them.
The strategist Li Zuoche advised Chen Yu to give him thirty thousand troops to take a back route and unexpectedly cut off the Han army's supplies and food. Meanwhile, when the Han vanguard reached Jingxing, the main Zhao force should avoid battle. Following this plan, he claimed, they could capture the heads of Han Xin and Zhang Er within ten days.
Chen Yu, however, was a scholar who disliked using deceitful or unconventional tactics. He believed Han Xin's forces numbered only in the thousands and were already exhausted from a long march of a thousand *li*, so they could be directly attacked. Thus, he rejected Li Zuoche's strategy.
When Han Xin's spies learned of this, they were greatly pleased. Confidently, Han Xin advanced eastward down Jingxing, stopping thirty *li* from the pass to rest. At midnight, he selected two thousand light cavalry, each carrying a red banner, and sent them along a hidden path to conceal themselves behind the mountains near Jingxing Pass. He instructed them: "I will send another force to confront the Zhao army and pretend to retreat. When the Zhao army sees this, they will surely abandon their camp entirely to pursue us. Seize this opportunity to rush into the Zhao camp, pull down their flags, and erect our Han red banners."
Next, Han Xin dispatched ten thousand troops to form a battle line with their backs to the river. The Zhao army, seeing the Han troops adopt the "back-to-the-river" formation—a tactic considered the most inadvisable in military strategy—burst into laughter, believing the Han army had cut off its own retreat.
At dawn, Han Xin led this ten-thousand-strong force toward Jingxing Pass. The Zhao army immediately opened their gates to attack. After a period of fighting, Han Xin and Zhang Er ordered their troops to abandon their flags and drums and retreat toward the river. The Han soldiers, now backed against the riverbank with no place to retreat, had no choice but to fight desperately.
At this moment, the two thousand Han cavalry hidden behind the mountains, seeing the Zhao camp undefended, swiftly charged into the Zhao encampment. They quickly pulled down the Zhao flags and replaced them with the red banners of the Han army. Meanwhile, the Zhao soldiers fighting by the river, unable to overcome the fiercely resisting Han troops who were fighting with their backs against the water, attempted to retreat to their camp. But upon seeing it filled entirely with Han red flags, they believed the King of Zhao had already been captured. Morale collapsed instantly, and the Zhao troops scattered in panic. Seizing the moment, the Han army launched a pincer attack from both sides. The result was the death of the Zhao commander Chen Yu and the capture of the King of Zhao.