Closed Gate

The Xuanwu Gate incident was a little-known event in Chinese history that could have changed the course of Chinese history, or even the course of the world's history. The Xuanwu Gate was a palace coup, in which China's to-be emperor Taizong killed two of his siblings, and forcing Emperor Gaozu of Tang to give up his place as emperor.

In this timeline, Li Jiancheng would become emperor of the Tang dynasty after his father's death in 635. Taizong was quite militant, declaring numerous wars during his reign as emperor. Korea, Uyghurstan, and Mongolia have extremely different histories in this timeline.

In terms of dynasties, China's entire history would be changed, as the incident occurred early in the dynasty's history rather than when it was destined to fall. The Mongol Empire would also never rise, as the Mongol rise to power was partly due to the Chinese states at that point. Western Russia would remain occupied by various city-based states, and the Siberian tribes would form their own united nation.