Emperor Yang Guang of the Sui Dynasty has always existed as a tyrant in history and people's impressions, and many people criticized him for his great achievements, making the Sui Dynasty a short-lived dynasty. During Yang Guang's reign, he went to Goguryeo three times, and these three campaigns led to the weakening of the Sui Dynasty's national strength, and it was also an important reason for the fall of the Sui Dynasty. But throughout history, not only Emperor Yang of Sui, but also several emperors after the Tang Dynasty also regarded Goguryeo as a great danger and used troops many times
Goguryeo is located in Southeast Asia and has a long history. During the Cao Wei period, due to the civil strife in the Central Plains, Goguryeo took the opportunity to develop rapidly, and during the chaotic period of the Central Plains of the Northern and Southern Dynasties, Goguryeo entered its heyday under the rule of King Haotai. As a neighbor of the Central Plains, Goguryeo showed its own ambitions, and had conflicts with the Central Plains Dynasty during the Cao Wei period. At that time, Goguryeo, which was in the period of development and growth, united with the Cao Wei regime to jointly attack Liaodong, but suddenly terminated cooperation in the middle of the process, and also attacked the areas where the Cao Wei regime was in the eastern and western parts of Liao. In order to take revenge, the Wei State launched an army to the east and almost destroyed Goguryeo, so Goguryeo put away its fangs and showed respect for the Central Plains regime, which was stronger than itself. However, after more than 40 years of recuperation, Goguryeo once again showed its restlessness, disobeyed the vassals of the Sui Dynasty, and raised troops to attack Liaoxi, thus triggering the Sui Dynasty's expedition.
Judging from the history of Goguryeo and the Central Plains Dynasty, it is not difficult to find that Goguryeo has always been a "wolf" waiting for an opportunity to develop and ambitious, it is dormant in the frontier of the Central Plains regime, if it is allowed to develop and grow, it will be another Liao State and the Manchu Dynasty, and the consequences will be unimaginable. Therefore, Emperor Yang of the Sui Dynasty went on many expeditions, not simply because of his love of killing and great achievements, but more because of practical considerations and to prevent trouble. Of course, in addition to uncontrollable factors such as natural and man-made disasters, his decision-making mistakes are also inextricably linked.
After Emperor Yang of Sui, Tang Taizong and others were always vigilant against Goguryeo, and also sent troops to recruit troops many times. Finally, in the 7th century AD, the Tang Dynasty joined forces with Silla Lianni and succeeded in destroying Goguryeo.