A:The intensive construction of the Great Wall since the Qin Dynasty (221-206BC) cost a lot of labor and human life, but the resulting consolidation of frontier defense saved even more people.
When the nomads were strong, they attacked and plundered the Central Plain on a large scale. When weak, they made small-scale, harassing raids on farming areas. The large-scale expeditions of the agrarian regime were effective against the large regiments of the nomadic regime, but had little effect on its scattered disturbance and looting. Therefore, the cost of building a wall for stabilized defense was much less than the cost of mounting full-scale wars. All wars, just or unjust, offensive or defensive, always end up with destruction whether in victory or defeat. To put it simply, the ancient Chinese built the Great Wall to avoid more wars and harassment on both sides.
No dynasty in ancient China had sufficient military and economic power to maintain the normal production and life of the vast area of northern China through garrisons of troops alone. On the contrary, building a Great Wall, although costly, significantly reduced the need for the central regime to maintain a long, heavy military presence in the region, or to launch military counterattacks, as the Wall would have largely deterred small, frequent, harassing cavalry raids and significantly slowed down large-scale attacks from the north by the use of early warning signals from nearby defensive troops. The Great Wall was and remains a measure to maximize long-term benefit at minimum cost.