According to historian David Curtis Wright in his book The History of China, the Qin (221-206 BCE) and Han (202-220 CE) dynasties were responsible for building the Chinese empire through unification. Wright describes the Eastern Zhou period as "chaotic and divided" (45). Qin, a neighboring state to Zhou, created unity in China by dominating Zhou militarily. Hence, the factors that led to Qin's military victory are some of the most important factors that led to the establishment of the Chinese empire.
One factor contributing to military success is that Qin's geography served as a natural barrier preventing Qin's enemies from conquering the state. Qin was located in the Wei River valley, bordered by the Qin Mountains, also called the Szechuan Alps. A second factor contributing to Qin military success is that, as Wright phrases it, the "Qin government was also an aggressive recruiter of administrative and military talent" (46). Qin established Legalism as its ideology, a Chinese philosophy that focused on strictly applying laws to restrain mankind's inherently evil nature ("Legalism," Encyclopaedia Britannica). Qin Legalist administrators created a united state by doing away with feudalism so that the one, unified government could benefit from "all of the tax revenue from agriculture" (46). Legalist administrators also abolished aristocratic titles and replaced the system of aristocracy with a system in which civilians and military personnel were promoted based on their own merits, a system that created a very strong government and military. Dissolving feudalism and aristocratic titles was one step that leading to a unified China.
The dictatorial Emperor Qin Shihuang made huge strides in unifying China by eliminating cultural differences by opposing "Taoists and Confucians as subversive," by burning books that were not Legalist, by executing 400 highly educated persons who opposed Legalist thought, and by creating standard "coinage, weights, [and] measures" (46-47). Tyrannical Legalism soon naturally led to rebellion, which led to the fall of the Qin dynasty. The next dynasty, the Han dynasty, abandoned Legalism altogether.
During the Han dynasty Liu Bang ruled as "one of the only two commoners in Chinese history" to become emperor (50). Due to his empathy for the commoner, he lowered taxes and the number of capital offenses, helping create a happy, healthy, economically prosperous Chinese society that was unified because the Qin dynasty had already unified it through its Legalist and totalitarian government. Emperor Wudi, which translates, according to Wright, as "martial emperor," was Liu Bang's succeeding emperor and is recognized as the "greatest Han emperor" (51). Emperor Wudi took several steps to strengthen China into a unified empire. His first step was preventing excessively wealthy merchants from acquiring land, which he feared could lead to a return to the feudal system. His second step was conquering the Xiongnu, China's frequent enemy, leading to an expansion of China's borders. His third step, one of Emperor Wudi's greatest contributions to building the Chinese empire, was making Confucianism the "official state ideology," which unified and structured the Chinese government under a set of moral ideals and principles of social hierarchy; Confucianism would remain China's governing ideology until its overthrow in 1911.