It was the middle of class when armed men burst into a school one morning in December 2013 in the town of Rubkona, in South Sudan’s Unity State. Pointing their weapons at bewildered pupils, the men forced scores of teenage boys to climb into military trucks that had pulled up outside. Across town, in another Rubkona school, similar scenes were unfolding. There was no time for the boys to object, or to say goodbye to their families. Then, as suddenly as they’d arrived, the trucks tore away, carrying inside them hundreds of boys ages 14 to 17.