Map of the Kingdom's Warfare.

Summary

The Sui army quickly built a wall to block the Tang army's advance in Hengshan Valley. Zhang Xuan, observing from a distance, recognized the strategic advantage this provided, as he aimed to capture Duan De Cao's capable leadership for future plans. Despite the Tang army's attempts to fortify their position, they were ambushed by Sui cavalry, leading to chaos and mass surrender among the Tang soldiers. Liang Li, witnessing the defeat and the death of his comrade Cheng Duo, felt the weight of impending consequences from the emperor. As morale plummeted among the Tang troops, Duan De Cao faced a dire situation, realizing escape was impossible. After discussions with Liang Li, they received a letter from Zhang Xuan, which ultimately led to Duan De Cao's decision to surrender. The next day, he and his troops surrendered to the Sui, resulting in their integration into the Sui army, while Zhang Xuan continued his campaign westward.

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