In some very important respects, the institution of war is clearly in decline.
Certain standard, indeed classic, varieties of war have become so rare that they could well be considered to be obsolescent, if not obsolete. Most notable has been the waning of major war--war among developed countries--roughly following the pattern by which slavery became discredited and then obsolete. This process has depended far more on changing attitudes toward war than on technological developments such as the invention
of nuclear weapons. Also in decline, it appears, are conventional war more generally, conventional civil war, colonial war, and ideological civil war.
Moreover, what is currently labeled "war" or "new war" (or, most grandly, "clashes of civilizations") is often more nearly opportunistic predation waged by
bands--often remarkably small ones--of criminals, bandits, and thugs, and sometimes of children. The damage perpetrated by these marauders--who, as in Yugoslavia, commonly apply ethnic, nationalist, or religious rhetoric--can be extensive, but it is often scarcely differentiable from crime. Most notably, where governments are weak, crime tends to surge, and particularly where there are, in addition, exportable resources, crime will require substantial organization and will sometimes look like war. It is hardly a new phenomenon in human history: indeed, it is quite ancient and, at base, thoroughly elemental.
To a substantial and perhaps increasing degree, then, warfare has been reduced to its remnants--or dregs--and thugs are the residual combatants. The key to its existence is government effectiveness, not ethnic tension. Some evidence suggests that even this kind of armed conflict may be in decline of late.
Since thugs tend to be opportunistic and cowardly, policing them would generally not be very difficult or costly for almost any organized, disciplined, and sizeable army. However, the misguided assumption that such conflicts stem from immutable ethnic hatreds and an extreme aversion to casualties make international military intervention highly problematic politically.
The waning of war seems to be associated with long term declines in certain kinds of visible, public killing--human sacrifice, blood feuding, dueling, homicide, capital punishment. At the same time, however, there has been continued, and even increasing, tolerance for some forms of deliberate killing that are non-violent, indirect, or hidden from view.