China, due to its geographical environment, is really a country with open doors and irrelevant things, and it is difficult to close itself in political and economic terms.
Therefore, in ancient China, the biggest headache for the Central Plains Dynasty was the threat of the border. During the Sui and Tang dynasties, Goguryeo, which was active in the northeast region of China, was a major hidden danger affecting the security of the Sui and Tang borders. Even, in order to maintain the stability of the frontier, the emperors of the Sui and Tang dynasties sent troops to conquer Goguryeo.
But why did the later Tang Dynasty succeed, but the Sui Dynasty fail? This has to be said about the strategy adopted by the Tang Dynasty.
Although force is the easiest and most effective way to solve problems, not all thorny problems can be solved with it.
Goguryeo, after king Haotai ascended the throne, its dynasty entered a period of heyday. During this period, King Haota conquered many surrounding tribes and small kingdoms, and made Silla his vassal state. In 427, king Changshou of Goguryeo took the throne, and he moved the capital from present-day Jilin Province to the Korean Peninsula, where he was the capital at Pyongyang.
From the end of the 6th century to the beginning of the 7th century, Goguryeo began to fight frequently with the Sui and Tang dynasties. The king of Goguryeo advocated the exchange of war for peace, and his exhaustive military force posed a great threat to the people of the northeast border, causing the people in this region to suffer unspeakable, and even the rise of Goguryeo made the northeast border very unstable.
However, at the turn of the Sui and Tang dynasties, Silla under Goguryeo control rose rapidly and captured part of the territory west of the Han River valley of Goguryeo, so that the outlet to the Yellow Sea was firmly controlled by Silla. Originally attached to Silla in Goguryeo, because of the access to the Yellow Sea, it could finally make its own decisions and directly trade with the Tang Dynasty.
When Goguryeo was strong, because of his heavy pressure, Silla wanted to ally with the Sui and Tang Dynasties to resist the powerful Goguryeo. However, Goguryeo found the Turks in the north as its strategic partners in the joint confrontation with the Central Plains Dynasty. Turkic is the collective name of the ethnic group that has been active in the Mongolian plateau and Central Asia in history, and the Sui and Tang Dynasties have been invaded by turks.
In April of the ninth year of Emperor Wen of Sui's reign, after the destruction of Southern Chen, the Sui Dynasty demanded that the surrounding countries submit to the Sui Dynasty. At that time, Goguryeo, which was in full swing, of course, would not yield, but on the contrary, it increased its efforts to expand its armaments and was ready to meet the army of the Sui Dynasty. In 589, in the nineteenth year of the reign of Emperor Wen of Sui, Goguryeo sent troops to preemptively attack Yingzhou in western Liaoning.
In this regard, Emperor Wen of Sui was furious and set out with an army of 300,000 to conquer Goguryeo. Later, because of the long distance, the army suddenly encountered heavy rainstorms, the road was difficult to walk, the marching speed was slow, the supply of materials was not enough, etc., the army's conquest of Goguryeo could only fail; on the other hand, the navy could not reach the Korean Peninsula because of the sea storm.
As a result, the Sui Dynasty's first conquest of Goguryeo could only end in failure.
By the time of the Sui Dynasty, the Turks had already submitted to the Central Plains Dynasty, and the Sui Emperor Yang Guang was a man who liked to travel around quickly, so he ran to tour the Turkic Khaganate. It was because of this inspection that the Sui Emperor discovered the two hearts of the Turks, and the Turkic Khaganate secretly had an alliance with goguryeo envoys. In this regard, the Sui Emperor was furious and immediately ordered the dispatch of troops to Goguryeo.
Therefore, in 612 AD, the Sui Emperor personally led an army of 300,000 troops, divided into two roads- land and sea, and simultaneously conquered Goguryeo. However, this conquest was once again met with strong resistance from Goguryeo, and the Sui army collapsed. Later, the Sui Dynasty launched another campaign against Goguryeo, but it was forced to stop because of the outbreak of a peasant uprising in the country.
After the Tang Dynasty succeeded to the throne of Li Shimin, Goguryeo still adopted a hostile attitude towards him. In order to defend the Tang army, they built a military in Liaodong. Because the Liaodong region was originally China's territory and could not be ceded to foreign nationalities, Li Shimin sent troops to the Liaodong region. However, in the early stages of the war, the Tang Dynasty did not win a decisive victory.
In order to be able to defeat Goguryeo quickly, the Tang Dynasty started with its ally, the Turkic Khanate, and first destroyed the Turks, leaving Goguryeo without backup. Later, the Tang Dynasty allied itself with Silla and joined forces against Goguryeo.
In addition, during the reign of Emperor Gaozong of Tang, the Tang Dynasty also saw the importance of the navy in the conquest of Goguryeo and began to increase its investment in the construction of the Tang navy. Because Goguryeo itself was on the Korean Peninsula, the Tang army would be exhausted after a long march, and it would become powerless to fight Against Goguryeo.
Therefore, it is imperative to strengthen naval construction, and after completion, the navy will be able to cross the sea from Shandong and directly reach the capital city of Pyongyang. By 660, the Tang Dynasty had conquered Baekje, leaving Goguryeo without allies and isolated. Moreover, there were also many pro-Tang elements in Goguryeo, and the power was huge, and if it was used slightly, it could achieve remarkable results, which was also a key step in achieving victory.
After all this was ready, the Tang army began to launch a conquest of Goguryeo.
In 666, Yuangai Suwen died, and his eldest son Yuanzi went to the front line to inspect the military situation, and was framed by his brother, saying that he had surrendered to the Tang Dynasty. Because their father, Wongai Suwen, was powerful in Goguryeo, won's younger brothers, Won-nam-jin and Won-o-chan, used their power to force the King of Goryeo to order the capture of his defecting brother. Cornered, Yuan Boy could only turn to the Tang Dynasty.
On the other hand, because the Yuan boys defected to the Tang army, the Tang army mastered all the military subordinates of Goguryeo, and even more Yuan boys led the way, and the Tang army was invincible all the way down. Those Goguryeo guards did not dare to resist when they saw that there were yuan boys in the Tang army, and most of the rest of the army surrendered except for a few recalcitrant troops.
Later, the Tang Dynasty took control of the King of Goguryeo and used his power to persuade many pro-Tang forces to surrender, and even the local monks took the initiative to open the gates of Pyongyang City and let the Tang army enter. After Tang Ping and Goguryeo, they were divided into nine governors, forty-two prefectures, and one hundred counties, and set up the Andong Capital Protectorate in Pyongyang to unify them. At this point, the problem of Goguryeo was perfectly solved.
The different strategies and tactics used in the conquest of Goguryeo also explain the differences in the results of the Sui and Tang conquests.
Resources:
[History of the North? Goryeo Biography, Dongyi Chuan Goguryeo, Old Book of Tang