Prison gangs are groups in prison or correctional institutions for mutual protection and advancement. Prison gangs often have several "affiliates" or "chapters" in different state prison systems that branch out due to the movement or transfer of their members. The 2005 study "neither War nor Peace: International Comparisons of Children and Youth in Organized Armed Violence" studied ten cities worldwide and found that in eight of them, "street gangs had strong links to prison gangs". According to criminal justice professor John Hagedorn, many of the biggest gangs from Chicago originated from prisons. From the St. Charles Illinois Youth Center originated the Conservative Vice Lords and Blackstone Rangers. Although the majority of gang leaders from Chicago are now incarcerated, most of those leaders continue to manage their gangs from within prison.