Another Possibility of the Great Tang

This novel is fictional; please don't take it seriously. In the early years of the Tang Dynasty, Xia King Dou Jiande led his army to rescue the besieged Wang Shichong in Luoyang. Just before the battle with the Tang army, Emperor Li Yuan of the Tang suddenly passed away. The Prince of Qin, who commanded heavy troops outside, the Crown Prince about to ascend the throne, and the ministers who chose sides, along with separatist forces, together staged an epic drama in a parallel universe... — Description from novelcodex.org