BASICS OF WARFARE
Warfare is a state of being in which an established behavior pattern is in a certain state of organized, violent conflict that is typically engaged in between two or more separate social entities. According to Sun Tzu, " The art of war is of vital importance to the State. It is a matter of life and death, a road either to safety or to ruin. Hence it is a subject of inquiry which can on no account be neglected." Sun Tzu, of course, quite literally wrote the book on the "Art of War"; which in that sense, war is truly an art, and truthfully not an exact science despite the extensive research, testing, and technology typically used and exploited in it's execution.
In the modern era, world wars and countless other major conflicts have changed the employment of the militaries beyond recognition to their ancient participants. Empires have come and gone; states have grown and declined. Enormous social changes have been wrought, and military power continues to dominate international relations. The role of the military today is as central to global societies as it ever was.
The manners and execution of such wars have drastically changed over the centuries; but their central theme and importance have not. Quite literally, any state that has not engaged in active warfare or defense in some form or another has either been destroyed, assimilated, or continuously protected by and external force, of which it is usually directly associated with. The reason for the global and wide-spread exploitation of warfare is primarily due to it's destructive nature; as such, most nations or states which haven't conducted in some aspect or another of warfare or armed defense have most likely been destroyed or already eliminated by the destructive aspects of war, meaning that most the remaining states, as a result of war, must have been war driven at some point in order to survive in modern day existence.
A a very good book to read in understanding, re-approaching, or generalizing basic aspects of the "Art of War", is of course, the Art of War by Sun Tzu. It teaches the basic concepts of the Art of War, and many lessons explained can still be applied today- mostly due to it's theoretical approach at situations, rather than blatant statements. For instance, when Sun Tzu talks of different kinds of Terrain, he doesn't merely speak of different environments, as environments can change and have continued to change historically; rather he talks of types of terrain, based on certain effects of the terrain, rather than the terrain itself. In this manner, and through broad generalization, Sun Tzu's "Art of War" serves as a very effective guide for the Art of War, in all aspects occupying all types of terrain and different kind of scenarios. The "Art of War" is so effective at being an applied system, rather than a simple guide to conventional warfare, that businesses, sports professionals, and people in many different kinds of competitive scenarios have learned to adapt the philosophies and ideas of the Art of War to their specific scenarios; even when their form of "warfare" is entirely abstract in nature. Sun Tzu's concepts, theories, and philosophies are based more so on objective qualities rather than subjective qualities, and adhere to certain fundamental truths that describe events that occur in a particular manner rather than the events themselves.
In addition, to those of which who seek odd forms of "Leadership", wish to have an objective viewpoint in terms of the abstract concept of power, or whom merely want to explore and read more material centered around concepts of war, the Prince by Niccolò Machiavelli is another good read. While not necessarily entirely about war, the read has more to do with power and the ways to maintain power (at the time, in warring states) and helps to emphasize events in leadership and "power". What is unique about the Prince is it's strict obedience to objective criteria rather than subjective criteria, and seeks to constantly achieve a goal based on reliable, in some cases somewhat consistently true information, and very truthfully "Machiavellin" approach; that is an approach to situations that disregards all other variables other than that of which will achieve the projected goal, sometimes the means to the end directly inflicting what would normally be considered "Great Evil" upon people. While not necessarily the most important read or something that should form the base criteria or philosophy of a leader, it does provide several key insights in leading and in terms of of exploiting, executing and maintaining power, serving as an objective set of criteria for leadership and power in general.