Before 642 AD, Goguryeo consistently maintained a low profile and submitted to the Tang Dynasty, but this did not mean Li Shimin had no designs on it.
Goguryeo was the catalyst for the downfall of the Sui Dynasty, and conquering it was the ultimate way to prove that the Tang Dynasty could surpass the Sui in every aspect.
It also represented a chance to defeat another man; the temptation was simply too great.
Chapter 255