OB-DRA - The Great Wall worked for China? Did you forget Genghis and his grandson Kublai Kahn? Mongols, they invaded and ruled all the lands from Japan to Eastern Europe. That included China, beyond the wall. Stationary defenses don't work, as every successful general and immigrant group has shown us, throughout history. As most of us here, descendants of Celts, Germans and Dacians, showed the Romans.