The main reason for the construction of the Great Wall of China was to protect against invasions from nomadic tribes and military incursions. Dating back to 7th century BC, various dynasties expanded and reinforced different sections of the wall over the centuries. The wall served as a defensive barrier, helping to secure agricultural lands and trade routes, particularly during the Qin, Han, and Ming Dynasties. Beyond military purposes, the Great Wall also facilitated the control of immigration and emigration, allowing for improved taxation and regulation of commerce, making it a symbol of Chinese strength and unity.