Slavery has been around the centuries but got more well known around this period of time and they used to the system to the advantage when they arrived
Up until the First Opium War, the foreign threats Han Chinese were used to dealing with were foreign nomadic invaders invading from the north. While Han Chinese were used to being occupied, even by foreign dynasties such as the Mongol Yuan dynasty, the foreign occupiers were always absorbed into the great ocean of Chinese culture and eventually disappeared.