(CNN) - For sheer cruelty, they are well matched. They also share an apocalyptic "end-of-days" vision. Now there are signs that Boko Haram -- the most feared group in West Africa -- may be edging toward a formal pledge of allegiance to the self-declared Caliph of the Islamic State, Abu Bakr al Baghdadi. Observers of Boko Haram, which has inflicted years of terror on northern Nigeria, note that its actions in the last six months have frequently mimicked those of ISIS -- from punishments such as stoning and beheading of its victims to taking territory and an increasingly sophisticated use...