What are the advantages of Koryo? Why didn't the Sui Dynasty win three expeditions?

In the first century, North Korea was still under the rule of the Han Dynasty. At that time, a Fuyu man from East Lake established a kingdom in Jilin, and Zhu Meng, a member of the royal family, went to northern Liaoning to establish Koguryo Kingdom because of the failure of power struggle. In the sixth century, the kingdom of Koguryo reached its peak. By the end of the 6th century, there was a three-legged pattern on the Korean Peninsula, with Koguryo in the north and Baekje and Silla regime in the south. Sui and Tang Dynasties were Silla's allies.

Although the Sui Dynasty only existed for 38 years, he attacked Koguryo four times. During the period of Emperor Wendi of Sui Dynasty, as Goguryeo and Mohong invaded the border of Sui Dynasty, Emperor Wendi sent 300,000 troops to northern expedition to Goguryeo. But because Goguryeo admitted her mistake in time and sent an ambassador to make peace, her words were better. Moreover, the plague broke out in the army of the Sui Dynasty, and food and grass could not be supplied, which led to the temporary suspension of the Northern Expedition. During the triumphant Emperor Yang Di's reign, Koguryo gradually hardened her wings, pretending to be a big country of agriculture and animal husbandry, and did not pay tribute to the Sui Dynasty, which seriously damaged the original tribute system and damaged the face of the Sui Dynasty as a big country.

Yang Di conquered Goguryeo three times, one was to teach Goguryeo a lesson and teach him how to be a man, and the other was to shock the domestic aristocratic groups. However, Emperor Yang Di conquered three times, but all ended in failure. Goguryeo has the confidence to fight against the Sui Dynasty. It has a vast grain-producing area, that is, the black land in the northeast, with changeable terrain, mainly mountainous areas and extremely cold climate. These are all natural environmental advantages that Koguryo can rely on. In order to get rid of the restriction of the gentry on its rule, Yang Di had to attack Koguryo and establish military achievements to deter these people. The biggest problem of sending troops from the Central Plains to attack Koguryo is that it is a long way, and it is necessary to bypass the entire Bohai Bay to enter Koguryo. It's a long way, and logistics supply becomes a problem. Coupled with the low degree of development in Liaodong area at that time, the land was barren everywhere, and the transportation was inconvenient, which led to the slow March of the Sui army.

Emperor Yang Di had to recruit civilian workers twice as many troops as his army to transport food. When Yang Di 1 expedition to Koguryo, the troops were1130,000, and there were more than 2 million civilian workers. The entire Sui government had to bear the supply of rations for 3 million people. The people's rebellion has begun to show signs. So many people have to eat, which brings serious pressure to the logistics supply line. During the busy farming season, all male laborers are recruited as laborers, resulting in a large number of fields being deserted. The three conquest of Koguryo became the last straw to crush the Sui Dynasty. Emperor Yang Di also recruited a large number of laborers to build warships for him. Shandong people soak in the sea every day, and their skin is soaked by seawater, which is also the reason for the first peasant uprising in Shandong Peninsula.