Han Xin, a brilliant general under Liu Bang, King of Han, devised a strategy to conquer the Guanzhong region, then crossed the Yellow River eastward, defeating and capturing Wei King Bao, who had betrayed Liu Bang to follow Xiang Yu, before marching east to attack Zhao King Xie.
Han Xin's army had to pass through a narrow mountain pass called Jingxing Pass. Li Zuoju, a strategist for the King of Zhao, proposed blocking the pass while sending troops along a hidden path to cut off Han Xin's supply lines, arguing that without reinforcements, the expeditionary force would surely retreat. However, General Chen Yu, confident in his superior numbers, dismissed the plan and insisted on a direct confrontation with the Han army.
When Han Xin learned of this, he was delighted. He ordered his troops to camp thirty li from Jingxing Pass, and at midnight, he gave them light snacks, promising, "Eat your fill after we win the battle." He then sent two thousand light cavalry along a hidden path, instructing them to charge into the Zhao camp once the enemy left, replacing their flags with Han banners. Meanwhile, he deployed ten thousand soldiers with their backs to the river, deliberately forming a vulnerable line to lure the Zhao army into attack.
At dawn, Han Xin launched his attack, and the two armies clashed fiercely. Soon, the Han forces feigned defeat and retreated to their riverside position. The Zhao army, abandoning their camp entirely, gave chase. At that moment, Han Xin ordered his main force to strike, while the soldiers arrayed with their backs to the river, having no escape route, turned and charged the enemy with desperate fury. Unable to prevail, the Zhao troops attempted to return to their camp, only to find it already covered with Han banners. Panic seized them, and they scattered in all directions. Han Xin's forces pressed the pursuit, securing a resounding victory.
During the victory celebration, the generals asked Han Xin, "The Art of War says formations should have mountains at their back and face water. But you had us line up with our backs to the river, saying we'd defeat the Zhao army and then eat our fill. We didn't believe it at the time, yet we won. What strategy was this?"
Han Xin laughed and said, "This is also found in the art of war, but you simply failed to notice it. Doesn't the art of war say, 'Place troops in a death ground and they will fight to live; put them in a hopeless position and they will survive'? If there were a way to retreat, the soldiers would all scatter—how could I make them fight to the death?"
This story evolved into the idiom "Back Against the River," often used for military operations, and also as a metaphor for decisive actions. Later, the idiom "Back Against the River" came to mean fighting to the death.
Source: *Records of the Grand Historian*, "Biography of the Marquis of Huaiyin"
Meaning of the Idiom: Later, the Chinese idiom "背水一战" came to describe fighting to the death.