Did the Great Wall serve its purpose of protecting China in history?
The Wall served well. Only when a dynasty had weakened from within, were invaders from the north able to advance and conquer. Both the Mongols (Yuan Dynasty, 1271-1368) and the Manchurians (Qing Dynasty, 1644-1911) were able take power, not because of weakness in the Wall but because of weakness in the government and the poverty of the people. They took advantage of rebellion from within and stepped into the void of power without extended wars.