Final answer:
The Qin Dynasty initiated the construction of the Great Wall of China to protect against invasions from northern nomadic tribes. Over time, the wall was expanded and reinforced by subsequent dynasties, serving both as a defensive structure and a symbol of territorial expansion and control.
Step-by-step explanation:
The Qin Dynasty began construction of the Great Wall of China to protect itself from invasion along its northern borders. The Wall was a defense against nomadic tribes such as the Hu (Donghu) and the Yuezhi, who posed formidable threats to the Qin territories. Initially, defensive walls were built as states expanded northwards into nomadic lands, but subsequently, it became a grander strategy to solidify control in these areas. The Qin Dynasty's Great Wall was part of a broader pattern of militaristic expansion, and subsequent dynasties continued the practice of wall construction, as seen with the Ming Dynasty walls, which are often what people refer to today when they mention the Great Wall.
Additionally, the Ming Dynasty's enhancements to the Wall around Beijing and Liaodong Province were part of a larger effort to safeguard against invasions, notably from the Mongols and later from the Manchurians. Over time, the Great Wall came to symbolize the division between the agrarian Chinese civilization and the nomadic cultures to the north, although in reality, the boundary was not so neatly defined. The walls enclosed new territory and, as the territory expanded, so did the need for defense, leading to further wall building.