Why is Qin so powerful?

I hope it helps you. Shang Yang's reform can not be simply regarded as a feudal reform, because the land system in Qin Dynasty did not become private, but was still state-owned, which was not much different from the land ownership in the slave society before. However, since the mid-Spring and Autumn Period, Qin has expanded its territory to the west, with a vast territory and a sparse population. The core policy of Shang Yang's political reform was "the battle of ploughing fields", so after the political reform, Qin actively absorbed the Kanto labor force and immigrated to Qin for farming. According to Shang Yang's legalist theory, people do things out of utility, and they can reward farming and develop production through rewards and punishments. Therefore, the enthusiasm of Qin people was mobilized, and agricultural production soon surpassed that of other countries. Obviously, Shang Yang's farming and war policy serves for farming and war. Shang Yang believes that if the country does not take the initiative to wage war, on the one hand, it will produce some idle people, which is not conducive to domestic stability and unity, on the other hand, it will consume the limited wealth of the country and corrupt the national atmosphere. Therefore, on the basis of strong agricultural production, Qin established a very strong army, and if Qin people want to get rid of the situation of humble poverty, they can only change themselves from the exploited class to the exploited class and master the means of production through farming and hard fighting. During the Warring States Period, Legalists were the main leaders of the political reform, but only Qin succeeded. This is because since the Spring and Autumn Period, Qin has continuously consolidated the centralization of monarchy, and there are few traces of patriarchal relations in slave society, so clan forces cannot control the monarch. The policy of Shang Yang's political reform protected the monarch's rights to the maximum extent and won the strong support of Qin people, so the political reform was successful in Qin.

In the east of Guanzhong Plain where Qin is located, there are long and narrow culverts and dangerous roads, and in the southeast, there is Wuguan Road in the crevice of Qinling Mountains. On both sides, Qin borders Wei and Chu respectively. At the beginning of Shang Yang's political reform, Qin first took control of Wei Yuanzhou in Hexi region by fraudulent means, thus completely grasping the only channel for Qin Xiangdong. On the other hand, Qin Chu is close to Wuguan. From the period of King Huiwen of Qin Dynasty to King Zhao of Qin Dynasty, the State of Qin completely drove Chu forces out of southern Shaanxi through diplomatic fraud and military strikes, thus completely controlling the road of Wuguan. In this way, Qin completely occupied the geographical advantage and laid a good foundation for the final reunification of Qin.