First, because of his personal ambition and desire to unify the six countries;
Second, because the former kings of Qin continued to expand their territory, they made historical preparations for their reunification of the six countries; In particular, the success of Shang Yang's political reform brought Qin into the era of absolute monarchy, and the separation of agriculture and soldiers made Qin not afraid of war, but longed for it.
Third, Qin has a solid material foundation. Qinchuan, 800 Li, has gained a bumper harvest due to irrigation in Zheng Guoqu, and there is food to support the long-term war; Fourthly, with the help of Li Si, the prime minister of Legalism, the State of Qin adopted the correct diplomatic strategy of making friends far away and attacking Lian Heng near.
5. A series of policies adopted by Qin State to attract talents are not exclusive, which makes most of the talents in the Warring States period belong to Qin State, and they are euphemistic and elegant.
6. The weapons manufacturing industry in Qin was very developed, and its strong bow, hard crossbow and sword were the most advanced weapons systems in all countries at that time. At the same time, Qin implemented a large-scale cavalry regiment, which opened the prelude to the era of cold weapons in which cavalry was king. In the most crucial battle of Changping, unifying the world, Zhao was divided into two by cavalry, thus encircling and killing;
Xunzi, a great imperial thinker, appeared before the unification of Qin. His thoughts integrated Confucianism and Legalism, reformed Confucianism and played a theoretical guiding role in unifying the six countries. Finally, a series of legalist systems of his disciple Han Feizi were finally implemented after the establishment of the State of Qin.