The vast inequalities of wealth on either side of the invisible boundary between the Arab world’s richest and poorest countries - Yemen and Saudi Arabia - have come to define the small town of Haradh in northwestern Yemen, where aid agencies are scrambling to help an increasing number of stranded and ill-treated African migrants. In addition to drugs and arms smuggling, Haradh is becoming increasingly infamous for its role in the trafficking of African migrants in search of work in Saudi Arabia.