1, what the people want and what the people want. After hundreds of years of war in the Spring and Autumn Period and the Warring States Period, the people long for reunification and a stable life. At the same time, the reduction of the number of vassal States is conducive to reunification.
2. With Shang Yang's political reform, Qin's national strength increased and became a rich country. After Shang Yang's political reform, the national strength of Qin was far above that of princes. After years of war, Qin has the strength to destroy six countries and unify the whole country.
3. The success of Qin strategy. In order to disintegrate the alliance between the six countries and Qin State, Qin State adopted the strategy of making a distant friend and attacking Lian Heng near, which made the six countries struggle with each other and gradually declined, unable to resist the attack of Qin State.