Map of the Kingdom's Warfare.

Summary

Liu Lan Cheng's army aimed to occupy Xiyang County, cutting off the Tang army's southern supply route. Sui general Zhang Li led troops to Junyang County, threatening Tang governor Li Zhongwen to open the city gates. Despite initial hesitation, Li Zhongwen complied, allowing Zhang's forces to infiltrate and attack, leading to the fall of Xiyang County. Meanwhile, Tang leader Li Shimin, engaged in battles elsewhere, was alarmed by the loss of supplies and the strategic implications of the Sui's success. He recognized his oversight in rear defenses and the urgency to retake the southern supply route. Generals advised him to act quickly, but Sima Zhang Gong Jin suggested focusing on key locations, particularly Xiyang and Hongnong counties, while considering the abandonment of less critical areas. Li Shimin grappled with the decision, particularly regarding Luo Yang, which he felt was essential to capture.

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