The Heavenly Khan, Emperor Li Er of the Tang Dynasty

I killed my brothers, forced my father to become the Retired Emperor, and was cornered by the Turks on the banks of the Wei River, where I signed a treaty beneath the city walls. Later, I became the Heavenly Khan. But until the day I died, I kept wondering: What was the difference between the Sui Emperor Yang, surrounded by Turkic arrows beyond Yanmen Pass, and me sitting atop the archery tower at Xuanwu Gate?