In the ancient history of China, two famous emperors, Emperor Taizong Li Shimin of Tang Dynasty and Emperor Yang Guang of Sui Dynasty, both regarded the conquest of Gaogouli as an important part of their foreign policy. The reasons behind this phenomenon are worth further exploration.

Firstly, we need to understand the geographical location of Gaogouli and the international environment at that time. Gaogouli, located in the northern part of the Korean Peninsula, was a powerful country in the Northeast Asia. It not only controlled abundant resources but also possessed strategically important geographical advantages. For the Central Plains countries such as Tang and Sui, the existence of Gaogouli undoubtedly posed a huge potential threat.

For Li Shimin, his reign was the heyday of Tang Dynasty, with strong national strength and elite troops. To safeguard the border security of the country and expand its influence, Li Shimin chose a policy of external expansion. Gaogouli, as an important country in the Northeast Asia, naturally became one of his targets. By conquering Gaogouli, Li Shimin could not only consolidate Tang's position in the Northeast Asia but also further demonstrate its military strength to other countries in the region.

For Yang Guang, his reign was the later period of Sui Dynasty, when internal conflicts within the country were intensifying. To divert domestic tensions and consolidate his own ruling status, Yang Guang chose a policy of foreign conquest. Gaogouli, being one of the powerful countries in the Northeast Asia, held high strategic value for Sui Dynasty. By attacking Gaogouli, Yang Guang hoped to expand Sui's territory, enhance his own prestige, and thereby consolidate his ruling position.

However, despite both Li Shimin and Yang Guang sending large armies to conquer Gaogouli, their results were vastly different. Li Shimin launched two campaigns against Gaogouli during the Zhenguan period and ultimately achieved victory, successfully incorporating Gaogouli into Tang's sphere of influence. On the other hand, Yang Guang launched three campaigns against Gaogouli during the late Sui and early Tang period but failed to achieve decisive victories due to various reasons, ultimately leading to the decline and fall of Sui Dynasty.

In conclusion, the reason why both Li Shimin and Yang Guang wanted to conquer Gaogouli was primarily due to its abundant resources and strategically important geographical location. For Li Shimin, the conquest of Gaogouli could consolidate Tang's position in the Northeast Asia; for Yang Guang, the conquest was to divert domestic tensions, expand territory, and enhance his own prestige. However, due to different historical backgrounds and personal abilities, they achieved vastly different outcomes in their campaigns against Gaogouli.

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