The first of two interrelated security threats is multifaceted inasmuch as it stems from a complex combination of religious, political, historical, cultural, social, and economic motivational factors caused by the growing predilection for carrying out mass casualty terrorist attacks inside the territories of "infidel" Western countries by clandestine operational cells that are inspired by, and sometimes linked to, various jihadist networks with a global agenda. The second threat is more narrowly technical: the widespread fabrication of increasingly sophisticated and destructive improvised explosive devices (IEDs) by those very same jihadist groups. These devices, if properly constructed, are capable of causing extensive human casualties and significant amounts of physical destruction within their respective blast radiuses. These dual intersecting threats within the recent European context are examined in an effort to assess what they might portend for the future, including within the U.S. homeland.