Li Shimin, the future Emperor Taizong of Tang, ambushes and kills his rival brothers Li Yuanji and Li Jiancheng in the Xuanwu Gate Incident.

Emperor Taizong of Tang, previously Prince of Qin, personal name Li Shimin, was the second emperor of the Tang dynasty of China, ruling from 626 to 649. He is traditionally regarded as a co-founder of the dynasty for his role in encouraging his father Li Yuan to rebel against the Sui dynasty at Jinyang in 617. Taizong subsequently played a pivotal role in defeating several of the dynasty's most dangerous opponents and solidifying its rule over China proper.

Li Yuanji, formally Prince La of Chao (巢剌王), more commonly known by the title of Prince of Qi (齊王), nickname Sanhu (三胡), was an imperial prince of the Chinese Tang dynasty. He was a son of the dynasty's founder Emperor Gaozu of Tang, and in the intense rivalry developed between his older brothers Li Jiancheng the Crown Prince and Li Shimin the Prince of Qin, he sided with Li Jiancheng and often advocated drastic actions against Li Shimin, including assassination. In 626, Li Shimin, fearing that Li Jiancheng and Li Yuanji were about to kill him, laid an ambush for them at Xuanwu Gate outside the palace and killed them. Li Shimin then effectively forced Emperor Gaozu to yield the throne to him.

Li Jiancheng (Chinese: 李建成; pinyin: Lǐ Jiànchéng; 589 – July 2, 626, formally Crown Prince Yin, nickname Vaishravana, was the first crown prince of the Chinese Tang dynasty. He was the oldest son of the founding emperor Emperor Gaozu and the crown prince after the founding of the dynasty in 618 CE.

The Xuanwu Gate Incident was a palace coup for the throne of the Tang dynasty on 2 July of 626, when Prince Li Shimin and his followers assassinated his brothers Crown Prince Li Jiancheng and Prince Li Yuanji. Li Shimin, the second son of Emperor Gaozu, was in an intense rivalry with his brothers. He took control and set up an ambush at Xuanwu Gate, the northern gate leading to the Palace City, within the imperial capital Chang'an. The Palace City (宮城) was located in the northernmost central part of Chang'an. In later years, it was known as the West Inner Palace (西内) and the Taiji Palace (太極宮), but these designations were not used at the time of the coup, according to Bingham 1950b, 261 There, Li Jiancheng and Li Yuanji were murdered by Li Shimin and his men. Within three days after the coup, Li Shimin was installed as the crown prince. About two months later, Emperor Gaozu abdicated and passed the throne to Li Shimin, who would become known as Emperor Taizong.