One of the ideas to emerge among security experts and even within the Pentagon after 9/11 is the idea that the events of that day have propelled warfare into a new era of warfare. Distinct from first generation warfare, emphasizing massed manpower, the second generation, which emphasized firepower, and the third, which focused on maneuver, the fourth generation of warfare is, essentially, a form of globalized insurgency.
Historian and strategist Dr. Antulio Echevarria believes that this conception is half-baked, and in Fourth-Generation War and Other Myths argues convincingly for a more critical appraisal of the theory of fourth-generation warfare, and somewhat less convincingly for its rejection.
Anyone following what happened in Iraq and what is happening now in Afghanistan would want to read this brief volume.