Two potent forces power the Ebola and ISIS epidemics that the media are ignoring. They're (1) breakdown of governing authority, and (2) dissolution of "social capital" -- ties of trust and cooperation that empower individuals, families, and others to forge coalitions and tackle common problems at the community level.
At the start of classes one year ago, I was having to explain to my students why the United States appeared to be on the verge of going to war against the Syrian government. At the beginning of this semester, exactly one year later, I'm having to explain to my students why the United States may be on the verge of going to war against Syrian rebels.
Today respected clerics exist here and there, but many Muslims see the absence of a single authority as one source of the weakness and paucity of Islamic vision in the Muslim world today. In an era when the West has repeatedly invaded Muslim countries, overthrown their leaderships, and commandeered their economic and energy sources over much of the 20th century, the weakness and lack of leadership in the Muslim world remains a vivid concern to Muslims. Thus when the term "caliphate" is invoked, it touches a chord in the historical sensibilities of many.