Insurgent groups known collectively as the mujahideen fought a guerrilla war against the Soviet Army. Up to 2 million Afghans lost their lives during the Soviet occupation. American professor Samuel Totten, Australian professor Paul R. Bartrop, scholars from Yale Law School such as W. Michael Reisman and Charles Norchi, as well as scholar Mohammed Kakar, believe that the Afghans were victims of genocide by the Soviet Union.