"Rather Than commenting on the specifics of the war with Iraq, I thought it might be a good time to lay out a framework for understanding that and other conflicts. I call this framework the Four Generations of Modern War. I developed the framework of the first three generations during the 1980s, when I was laboring to introduce maneuver warfare to the U.S. Marine Corps (USMC). The Marines kept asking, 'What will the Fourth Generation be like?' The result was an article I co-authored for the Marine Corps Gazette in 1989: 'The Changing Face of War: Into the Fourth Generation.'[…]. The Four Generations began with the Peace of Westphalia in 1648, the treaty that ended the Thirty Years' War. With that treaty, the state established a monopoly on war. Previously, many different entities had fought wars--families, tribes, religions, cities, business enterprises--using many different means, not just armies and navies. (Two of those means, bribery and assassination, are again in vogue.) Now, state militaries find it difficult to imagine war in any way other than fighting state armed forces similar to themselves."
Military Review: http://militaryreview.army.mil
Military Review (September-October 2004), p.12-16