This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book suggests that, even if we reject certain substantive elements of Carl von Clausewitz's thought, his approach to the subject can serve as a shining example to any student of war. The trinity, although complete in itself as a description of the nature of war, is built on a number of central suppositions. These are not explicitly stated in the paragraphs in which the trinity is presented, but are deemed by Clausewitz as fundamental to an understanding of war and are examined in other parts of On War. Underlying all of Clausewitz's thoughts on war is the human element the behaviour and interaction of humans in their social environment. Of all of wars dimensions, the human element is the most enduring. Clausewitz is ever at pains to emphasise this essential, yet easily overlooked reality.