The Northern Zhou Dynasty destroyed the Northern Qi and unified the North, ending the separatist regime for nearly half a century since the split of the Eastern and Western Wei Dynasties, saving the people from the suffering of war, rebuilding their homes and resuming production, thus promoting extensive political, economic and cultural exchanges and development in the whole North and laying a solid foundation for the future reunification of China. It can be said that without the unification of the Northern Zhou Dynasty and the Northern Qi Dynasty, there would be no later unification of the Northern and Southern Dynasties. Yu Wenyong, the emperor of the Northern Zhou Dynasty, was the British ruler in the Southern and Northern Dynasties. Just as he was planning to "flatten the Turks and settle the south of the Yangtze River" and realize the ideal of reunifying the whole country, he died unfortunately on the eve of the war.

Emperor Wendi of Sui Dynasty, the founding emperor of Sui Dynasty, was a very successful emperor. After the founding of People's Republic of China (PRC), a series of military, political and economic reforms were adopted, which enabled the Sui Dynasty to quickly complete the great cause of reunifying the north and the south, and its national strength was at its peak. After Yang Di ascended the throne, Yang Guang adopted the strategy of attacking from outside and defeated the surrounding forces such as Qidan and Tuguhun.

During the Sui Dynasty, Pei Ju, assistant minister of Huangmen, told me: "The land of Korea is also a country of solitary bamboo, which was sealed in the week. The Han Dynasty was divided into three counties, and the Jin Dynasty also unified Liaodong. " The land occupied by Koguryo regime here can be traced back to the Western Zhou Dynasty and down to the Wei and Jin Dynasties, and it is irrefutable that Liaodong is the territory of China.

At this time, Koguryo has become a relatively large country in northeast China, with its capital in Pyongyang, the hometown of Lang County, Henle, also known as Chang 'an City. Pyongyang is also known as the "three capitals" of Koguryo, together with the domestic city and Seoul. At this time, Koguryo people occupied most of Liaodong, and Koguryo was the hereditary Duke of Liaodong. Koguryo is the overlord of Liaodong and a powerful political power. The relationship between Koguryo and Sui gradually entered a state of war.

In 590, the King of Koguryo Plain "managed the army to accumulate grain, in order to defend the refusal", and attacked Sui and Liaodong areas on a small scale for many times. Koguryo maintained a tense and peaceful relationship with the Sui Dynasty. After the Northern Dynasties, Goguryeo was conferred the title of "King of Korea" by Emperor Wendi, Emperor Gaozu of Sui Dynasty. Due to the disintegration of Baekje and Silla Alliance at this time, the south of Koguryo was relatively calm. In 586, Ping Yuanjun moved its capital from Pyongyang to Chang 'an (now Pyongyang, North Korea) until Goguryeo died. It lasted for 83 years.

Because Koguryo attacked the northern frontier of Sui Dynasty several times in a small area. Sui Gaozu was very dissatisfied with this and wrote to Wang Gaotang of Pingyuan: "Wang said that the Liao River is as wide as the Yangtze River. Han, how many Chen States are there? If I had no education, I would blame Wang Qian for winning and order a general. Why bother? " . In 596, after Koguryo succeeded to the throne, Special Envoy Sui met with Special Envoy Koguryo in Turkey. Emperor Gaozu of Sui Dynasty sent a letter to Goguryeo, demanding that Goguryeo stop forming an alliance with the Turks and stop invading the Sui frontier year after year, expressing his submission to Sui. Although the infant king of Goguryeo accepted the ultimatum of Emperor Gaozu of Sui Dynasty on the surface, in 597, the infant king joined forces with Mohong to pre-emptively attack Sui's military station in Jizhou Road.

At that time, there were Baekje, Silla, Hong and other regimes in Northeast China, which had long surrendered to the Sui Dynasty. At the beginning of the Sui Dynasty, Goguryeo adopted the policy of submission to the Sui Dynasty in order to eliminate other small countries. However, with the strength of the Sui Dynasty, Koguryo gradually became afraid, so he joined forces with other countries to invade the Sui Dynasty.

In 598, King Koguryo led more than 10,000 cavalry to attack western Liaoning and was beaten back by Wei, general manager of Yingzhou. Emperor Wendi of Sui sent 300,000 troops to attack Koguryo by land and water. Later, due to the road and weather, food and grass could not be supplied, and he became ill. Nine of the ten Sui troops died. At the same time, King Goguryeo was awed by the military power of the Sui Dynasty and sent envoys to apologize, so Emperor Wendi of the Sui Dynasty stopped fighting and remained the same.

Although there was no substantial war in this expedition, it laid the groundwork for large-scale conquest in the future. At that time, the Sui Dynasty had conquered many ethnic groups in the west, north and south, and the domestic economy reached its peak, and Yang Guang was an ambitious man. It's only a matter of time before we go to war with Koguryo.