Broadly speaking, there seem to be two methods for developing combat forces-for successfully cajoling or coercing collections of men into engaging in the violent, profane, sacrificial, uncertain, masochistic, and essentially absurd enterprise known as war. The two methods lead to two kinds of warfare, and the distinction can be an important one.
Intuitively, it might seem that the easiest (and cheapest) method for recruiting combatants would be to...enlist those who revel in violence and routinely seek it our or who regularly employ it to enrich themselves, or both. We have in civilian life a name for such people-criminals...Violent conflicts in which people like that dominate can be called criminal warfare, a form in which combatants are induced to wreak violence primarily for the fun and material profit they derive from the experience.
Criminal armies seem to arise from a couple of processes. Sometimes criminals-robbers, brigands, freebooters, highwaymen, hooligans, thugs, bandits, pirates, gangsters, outlaws-organize or join together in gangs or bands or mafias. When such organizations become big enough, they can look and act a lot like full-blown armies.
Or criminal armies can be formed when a ruler needs combatants to prosecute a war and concludes that the employment or impressment of criminals and thugs is the most sensible and direct method for accomplishing this. In this case, criminals and thugs essentially act as mercenaries.
It happens, however, that criminals and thugs tend to be undesirable warriors....To begin with, they are often difficult to control. They can be troublemakers: unruly, disobedient, and mutinous, often committing unauthorized crimes while on (or off) duty that can be detrimental or even destructive of military enterprise....
Most importantly, criminals can be disinclined to stand and fight when things become dangerous, and they often simply desert when whim and opportunity coincide. Ordinary crime, after all, preys on the weak-on little old ladies rather than on husky athletes-and criminals often make willing and able executioners of defenseless people. However, if the cops show up they are given to flight. The motto for the criminal, after all, is not a variation of "Semper fi," "All for one and one for all," "Duty, honor, country," "Banzai," or "Remember Pearl Harbor," but "Take the money and run."...
These problems with the employment of criminals as combatants have historically led to efforts to recruit ordinary men as combatants-people who, unlike criminals and thugs, commit violence at no other time in their lives....
The result has been the development of disciplined warfare in which men primarily inflict violence not for fun and profit but because their training and indoctrination have instilled in them a need to follow orders; to observe a carefully contrived and tendentious code of honer; to seek glory and reputation in combat; to love, honor, or fear their officers; to believe in a cause; to fear the shame, humiliation, or costs of surrender; or, in particular, to be loyal to, and to deserve the loyalty of, their fellow combatants.