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Why did Li Shimin seize the Xuanwu Gate in 626?

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Taizong The Taizong emperor, detail of a portrait; in the National Palace Museum, Taipei.

Li Shimin seized the Xuanwu Gate in 626 as a preemptive strike during a critical power struggle for the Tang dynasty succession.

By 626, the rivalry between Li Shimin and his elder brother, the crown prince Li Jiancheng, had reached a breaking point. Li Jiancheng had previously attempted to eliminate Li Shimin and had actively worked to undermine his political influence by poaching his talented officials. When Li Shimin arrived at the capital to see off his younger brother, Li Yuanji, he discovered that both brothers were allegedly plotting to murder him.

In response to this immediate threat, Li Shimin led a small group of followers to seize the Xuanwu Gate—the northern entrance to the emperor’s palace—where he ambushed and killed both Li Jiancheng and Li Yuanji. Following this decisive military coup, he informed his father, the Gaozu emperor, who subsequently abdicated in his favor, allowing Li Shimin to ascend the throne as the Taizong emperor.