During the Sui and Tang dynasties, both dynasties did a similar thing, that is, the expedition to Goguryeo, but the results were very different. The Sui Dynasty emperor Yang Guang's three expeditions to Goguryeo all ended in failure, eventually triggering domestic contradictions and leading to the demise of the Sui Dynasty; however, the Tang Dynasty's five eastern expeditions succeeded in recovering Liaodong and occupying Goguryeo, and the Tang Dynasty became stronger and stronger. Then, the same expedition to Goguryeo, why did the Sui Emperor and Tang Taizong have completely different results?
The most direct reason is probably the disparity in military command ability between the Sui Emperor and Tang Taizong. Although Yang Guang, the Emperor of the Sui Dynasty, said that he was not a mediocre talent, and had also gone to the battlefield and established meritorious achievements, he was self-conscious, so he was so happy that he could not listen to the advice of his courtiers. During the First Crusade, the Sui Emperor divided the huge army into three provinces, but whenever there was an offensive military operation, it was necessary to inform each other between the three provinces, and to report to the Sui Emperor first. Although this practice made the army more disciplined, but the adaptability was too poor, once the war was frustrated, the intelligence department was in chaos, the entire army would be like a headless fly, I don't know how to be good, which is also the reason why the Sui Emperor's first crusade to Goguryeo suffered heavy losses.
In addition, the Sui Emperor also ordered that as long as Goguryeo surrendered, the Sui army must first be appeased and reorganized, and could not continue to attack. This order of the Sui Emperor caused the Sui army to be afraid of its hands and feet, and many cities in Goguryeo surrendered many times, but the Sui army was limited by the order and did not dare to attack, so that Goguryeo had a chance to breathe. However, when Goguryeo found the opportunity, it did not show the slightest mercy to the Sui army, and they built the corpses of the Sui army into a jingguan to deter the Sui army. Compared with the Sui Emperor, Tang Taizong Li Shimin was a general of hundred battles, and he was able to be humble and consultative, employ people without doubt, and give greater autonomy to the front-line generals, thus exerting the general's own ability. Compared with the two, the Tang army's battle results were naturally much better than those of the Sui army.
The basis of the war was national strength, which was the fundamental reason why Yang Guang and Li Shimin had different results in their crusade against Goguryeo. The Sui Emperor was not a emperor, and many of his measures, although beneficial in qianqiu, were too eager to succeed. Building canals, building palaces, and conquering Goguryeo in the east, the Sui Emperor did not stop for a moment, whether it was the people or soldiers, they were very dissatisfied with the Sui Emperor. However, after Tang Taizong Li Shimin ascended the throne, he recuperated and recuperated, and in the face of many foreign enemies, Li Shimin endured humiliation and signed a peace treaty with them. After Li Shimin succeeded to the throne, he used Taoist thought, which was quite the style of the Han Dynasty's "rule by doing nothing", and at the same time, he exerted great efforts to govern, selected the wise and the able, humbled and accepted advice, developed the economy, and finally created the "rule of Zhenguan". In the New Book of Tang, Ouyang Xiu of the Northern Song Dynasty praised Li Shimin and his rule of Zhenguan: "Sheng Zhao, Emperor Taizong's Lieye! Its chaos in addition to the Sui Dynasty is better than the Tang and Wu, and the beauty of Zhizhi, Shu Jicheng and Kang. Since the ancient merit and longevity, it has not been seen since the Han Dynasty. Ouyang Xiu compared Li Shimin to Tang and Wu, which is enough to show that Li Shimin has won the hearts of the people.
The Sui Dynasty Emperor's national strength before the Eastern Expedition to Goguryeo had been seriously depleted through the excavation of the Grand Canal, and his extravagant palace life also made the state financial income insufficient, so during the Eastern Expedition, the Sui Emperor could only rely on horizontal conquest, forced conscription and conscription to support his huge war. However, Tang Taizong first developed the economy, implemented the equalized field system, reduced taxes, and promoted the development of agriculture. At the same time, Tang Taizong took the lead in practicing strict economy, eliminating luxury, and the state finances improved rapidly. On the basis of the rule of Zhenguan, Tang Taizong and Tang Gaozong began their eastern crusade, with strong national support, even though Tang Taizong and Tang Gaozong carried out five eastern expeditions, more than the Sui Emperor, but the Tang Dynasty did not collapse.
Moreover, in the case of the disparity in national strength between the two dynasties, the scale of the war launched by the Sui Emperor was much larger than that of the Tang Dynasty. The Sui Dynasty Emperor's eastern expedition to Goguryeo was not imminent, but he ordered officials to urge the laborers to build warships as soon as possible. Under the supervision of the Sui Dynasty Emperor's edict, shipbuilders worked day and night in the water, "officials supervise, stand in the water day and night, slightly dare not rest, maggots are born from the waist down, and the deceased is shisan and four" (Zizhi Tongjian). In addition, the Sui Emperor, in order to promote the prestige of the country, did not hesitate to pour all the strength of the whole country, he gathered most of the troops of the whole country, and at the same time recruited millions of people, so many that they caused trampling, and the Zizhi Tongjian recorded: "In the past, hundreds of thousands of people were still in the Dao, filling in the Dao, day and night, the dead were sleeping with each other, the stinky road was full of filth, and the world was in turmoil." "Before the war has even begun, there are already countless people and soldiers who are tired alive and dead, so how can the people's grievances not boil? Coupled with the stupid command of the Sui Emperor on the battlefield, can the war not be lost?
However, compared with the Sui Emperor, Tang Taizong's eastern expedition to Goguryeo only sent about 100,000 troops, not even one-tenth of the Sui Emperor. Tang Taizong even refused to take the initiative to participate in the eastern crusade, and only led the elite army and water army. The small number of troops makes logistics much simpler and the flexibility of the army is also high. Therefore, Goguryeo could make the so-called millions of troops of the Sui army collapse, but it could not defeat the Tang army of only 100,000. Later, Emperor Gaozong learned from his father's experience, controlled the size of the army, and reduced the attrition of the war. The Tang Dynasty's national strength through Zhenguan was much stronger than that of the Sui Dynasty, coupled with the small losses of the Tang Dynasty's wars, the final result was naturally very different.
In addition, the different personalities of Tang Taizong and the Sui Emperor also led to different results. Goguryeo was good at defending the city, and both the Sui Emperor and Tang Taizong did not achieve their strategic objectives due to insufficient offensive capabilities when attacking Goguryeo, but the reactions of the two were completely different. After the failure of the First Crusade, the Sui Emperor became angry and immediately prepared for the Second Crusade, but Tang Taizong understood that the crusade against Goguryeo could not be completed in one battle, so he changed his strategy and implemented the tactic of attacking with partial divisions. Under the constant attacks and harassment of the Tang army, Goguryeo had to use all the troops, and the national strength was seriously depleted. Eventually, during the reign of Emperor Gaozong of Tang, he completely occupied the entire Liaodong and Korean Peninsulas.
In fact, the Sui Emperor made huge mistakes in tactics and strategy, he did not combine national strength, did not analyze the war situation in detail, was self-conscious, and insisted on going his own way, which eventually led to sharp domestic contradictions and the eventual demise of the Sui Dynasty. Tang Taizong witnessed the demise of the Sui Dynasty and the people of the world did not have a good life, so he learned the lesson of the defeat of the Sui Emperor, first developed national strength, created the rule of Zhenguan, and then adjusted tactics and strategies according to the war, and finally succeeded.
Resources:
New Book of Tang
"Zizhi Tongjian" Sima Guang