The Pre-Qin period was the time when the concept of "unitary state"was given birth to. In the Xia and Shang dynasties, the imperial power and autocracy came into being and further developed. The expansion of territory by the above-mentioned dynasties laid the foundation for the establishment of a unitary state. The Western Zhou Dynasty greatly expanded its territory by conguering Situ and siguo and became a vast country. During the Warring States Period the centralized states established and the political, economic and military systems of different states gradually became unified, thus forming early unitary state structure.