Liu Bei attacked Wu for revenge — Lu Xun burned his army and Shu never recovered

In 220, Guan Yu, Liu Bei's sworn brother and Shu Han's most feared general, was captured and executed by Sun Quan's Wu. To Liu Bei, this was not a military loss — it was a personal betrayal. He swore revenge. His two most trusted advisors both counselled against it. Zhuge Liang, the architect of the Longzhong Plan, argued that Shu should attack Wei, the main enemy, not Wu. Zhao Yun, the veteran general, gave the same advice: the enemy is Wei, not Wu. Liu Bei would not listen.

In 221, Liu Bei personally led an invasion of Wu with what remained of Shu's finest army — perhaps 40,000 to 50,000 men, including the veterans who had followed him for decades. Initially the advance went well. Liu Bei drove deep into Wu territory, pushing into the gorges of the Yangtze. Sun Quan appointed the young general Lu Xun to oppose him. Lu Xun refused to engage, retreating deeper and adopting a scorched-earth strategy. The long supply lines, summer heat, and impatience began to wear on the Shu army.

By the summer of 222, Liu Bei had advanced to Xiaoting (夷陵) in modern Hubei. His supply lines were stretched. The heat was unbearable. He ordered his army to move into the forests for shade and established a chain of camps stretching more than a hundred kilometres, each connected to the next through the wooded hills. Senior officers warned him that encamping in forests was dangerous — that a fire could spread through the connected camps faster than any army could respond. Liu Bei dismissed them.

Lu Xun had been waiting for exactly this mistake. He ordered a coordinated fire attack. The flames jumped from camp to camp through the connected forest. The Shu army, trapped between fire and Wu soldiers, was annihilated. Thousands died in the inferno. The survivors were cut down as they fled. Liu Bei barely escaped to Baidi (White Emperor City), where he died the following year. The veterans who had built Shu Han were gone. The kingdom would never be a serious threat again.