Border Wars and Climate Change: The Impact on the Evolution of the External Defense System of the Hexi Corridor in the Past 2000 Years

This study establishes a dataset of ancient military defense system sites in the Hexi Corridor area from the Han Dynasty to the Qing Dynasty to analyze the temporal changes and spatial distribution characteristics of the military defense system in different periods. In addition, it compares the climate characteristics of the Hexi Corridor area though the past 2000 years. It also discusses the possible relationship between the construction of the Hexi military defense system and climate change. We found that the Han and Ming Dynasties were the main periods for constructing the regional military defense system. Furthermore, the Wei, Tsin, and Southern and Northern Dynasties expanded the scale based on the previous period. As a result, the spatial distribution was highly concentrated. During this time, multiple cold–dry and warm–humid periods occurred in the region. Moreover, significant climate change coincided with the heyday of building military facilities and the period of frequent warfare. Environmental factors have an impact on the spatial distribution of military sites. Therefore, the northern border war was the direct cause of the construction of the military defense system. However, the transformation of the environment caused by climate change was the fundamental driving force for this process, evolving across different eras.