This paper focuses on the correlation between local socioeconomic development and state-making process across regions. Regardless of development gap between regions, local socioeconomic changes do have impacts on the size of the higher aggregated polity. In this paper, I construct a model introducing various socioeconomic factors jointly. The model concludes that increases in external threats, labor input in production and aggregated output may facilitate formation of large countries. On the other hand, higher unification cost and stronger military force at regional level lead to small countries. The implications are supported by Chinese historical evidence. For each province in ancient China, when it had high agricultural output, concentrated residence, and was vulnerable to severe natural disasters, the region was more likely to be united into a large country. Meanwhile, high military efficiency at regional level led to formation of small countries.