Why did all kinds of advanced and ingenious military etiquette and ideas prevail during the Spring and Autumn Period and the Warring States Period?

During the Spring and Autumn Period and the Warring States Period, it was a transitional period from feudal landlord system to feudal landlord system. The struggle between the old and new classes and between classes is complex and fierce. Scholars or thinkers representing all classes, strata and political forces try to explain or put forward opinions on the universe, society and everything according to the interests and requirements of their own classes (strata) or groups. Coupled with the social atmosphere at that time, "representing the interests of all classes", many people and things appeared. However, this era is short-lived. By the end of the Warring States Period, Legalists had begun to rise and successfully applied them to the State of Qin, eliminating the other six countries, establishing a centralized system, and making China a feudal country. During the reign of Qin Shihuang, many measures were taken to strengthen centralization and suppress other schools, leaving only legalists, which made the social atmosphere left over from the Spring and Autumn Period and the Warring States Period disappear. Since the state of Qin, emperors of all dynasties have strengthened centralization.