In 230 BC, the general Nei Shi Teng, the general of the Qin Dynasty, led an army to attack Korea, thus officially opening the curtain on the unification of the six kingdoms of Qin. After nearly ten years of conquest, the State of Qin successively destroyed Korea, the State of Zhao, the State of Wei, the State of Chu, the State of Yan, and the State of Qi, and successfully unified the world. So the question is, why did the Qin dynasty destroy the six kingdoms from Korea to the end of the State of Qi, and what is the order of this annihilation?
The first target of the Qin state was selected in Korea for two main reasons. First, South Korea's strength is the weakest in the "Seven Heroes of the Warring States"; second, South Korea is located in the heart of the Central Plains, curbing the way for Qin to go out of the Hangu Valley and advance eastward. Therefore, the Qin state first pinched the "soft persimmon" of South Korea, which can not only take the lead in breaking the balance pattern of the "Seven Heroes of the Warring States", but also enhance the confidence of the qin army generals. To put it bluntly, South Korea was given to the Six Kingdoms of Qin to practice.
The second target of the State of Qin was chosen in the State of Zhao. At that time, Zhao Guo's strength was among the best in the "Seven Heroes of the Warring States", and there were super famous generals such as Li Mu in the country. So why didn't Qin Guo continue to pinch "soft persimmons" and choose such a hard stubble as Zhao Guo? There are two main reasons.
First, the State of Qin was bordered by the State of Zhao to the north and the State of Chu to the south. The Qin army had to move one of these two mountains out of the east to avoid falling into the disadvantageous situation of fighting on both sides. The territory of the Chu state is vast, the waterways within the territory are longitudinal, the terrain conditions are complex, and the time and difficulty required for Qin to destroy Chu are greater than the time and difficulty of destroying Zhao, so under the same circumstances, qin state still chose a relatively easy goal.
Second, Qin and Zhao went to war, and powerful countries like Qi Chu would hold the attitude of sitting on the mountain and watching the tiger fight, hoping that one would be killed and the other would be crippled, and they would reap the benefits of the fishermen themselves. For example, in the "Battle of Changping" that year, the State of Qin severely damaged the State of Zhao, and it was also seriously injured and forced to stop the pace of expansion. And Qin's attack on the State of Wei is like swallowing a piece of fat meat in his mouth, which will not only not deplete the national strength, but will make it further strengthen. This was an unacceptable outcome for the other princely states, so they would be forced to intervene jointly. Moreover, Zhao Guo's appeal among the countries at that time was also one of the best. As long as Qin can successfully attack and destroy the Zhao state, the overall situation of unifying the world will be basically laid.
The third target of the Qin state was to choose the state of Wei, which was actually to beat the rabbit with grass. Because after the destruction of Zhao, Qin's main opponent was the State of Chu in the south, and the State of Wei was exactly at the junction of Qin and Chu. Although the State of Wei was already very weak at that time, the State of Qin did not want to attack the State of Chu while also preventing the State of Wei from sneaking attacks. Instead of worrying about it, it was better to attack it first, so the State of Wei only persisted for 3 months before perishing.
It was logical for the fourth goal of the Qin state to choose the state of Chu. At that time, the three kingdoms of Han, Zhao, and Wei had all been destroyed. The national strength of the Yan state was similar to that of Korea, and it was impossible to pose a substantial threat to the qin state. Although the State of Qi was strong, Wang Jian of qi was a fool, and he thought that as long as he did not offend the State of Qin, Qin would not be able to strike at the same level.
The Battle of Qin and Chu lasted for two years, and at first the Qin general Li Xin led a 200,000-strong army to cut down Chu, but the result was first victory and then defeat, with heavy losses. After that, the Qin general Wang Qi led an army of 600,000 to cut down Chu again, which made it difficult to bite the "hard bone" of the Chu state. From the process of the Battle of Qin and Chu, it can also be seen that the annihilation of the Six Kingdoms by Qin was not a completely crushing victory, so the choice of the order of annihilation of the country was crucial.
After Han, Zhao, Wei, and Chu were defeated one after another, there was no difference between the remaining Yan and Qi countries who fought first and who they fought later. Although the State of Qi was also a powerful country in the "Seven Heroes of the Warring States", it was not at all an order of magnitude compared with the State of Qin at this time. Therefore, the State of Qin first easily destroyed the State of Yan, which was already dying, and then went south from Yan to the capital of the State of Qi, Linzi. Only then did Qi WangJian suddenly wake up, but it was too late. In the face of the step-by-step pressure of the Qin army, the State of Qi surrendered without a fight, and the State of Qin thus completed the great cause of unifying the world.
References: "Records of History", "Zizhi Tongjian"