A very longstanding feature of my gameworld Celduin is that -- many long centuries ago -- the religion of the god Upuaut (the fire/war god of the pantheon) imposed something of a cross between the Geneva Conventions and a code of honor on the conduct of mercenaries in war. Subsequently interpreted and amended over the years, it's widely honored to the present day.
Honorable actions are not mandatory; dishonorable actions are to be always avoided. Actions that are not dishonorable are legal, but not the path of greatest honor. Obviously, some tenets are more honored in the breach than in the observance.
For those of you scoring at home, a “paktun” is a warrior of great prowess and honor, voted the accolade on the battlefield by the collective paktuns there present; they wear a distinctive silver medallion on a rainbow ribbon. “Nikobi” (half-oath) is the contractual arrangement between mercenaries and their employer.
- It is dishonorable to betray your employers, explicitly or implicitly. It is dishonorable to disobey direct orders. Obeying the laws of the nation under which you serve is honorable; obedience of an order in clear conflict with the law is a matter of conscience, but following the order is the path of greater honor, unless the order itself be dishonorable.
- It is dishonorable to slay or enslave soldiers who have surrendered, or to directly assist those doing so. It is honorable to disobey orders to do so. It is not dishonorable to loot the defeated or conquered territory.
- It is not dishonorable, under threat of certain doom, to surrender one’s command to a superior foe. To do so is a matter of personal conscience. It is dishonorable to knowingly lead one’s troops into certain death, and honorable to disobey orders to do so. It is not dishonorable to lead volunteers into such situations in order to protect a line of retreat.
- Lord Upuaut is our patron, and his servants and priests are honored by every true warrior. It is highly dishonorable to knowingly harm any of His priests, or any healer or physician. It is not dishonorable to defend yourself against an attack by a priest or physician, but you should seek to subdue him without killing. Priests fighting in battle forfeit such protection.
- It is dishonorable to harm any civilian without just cause. Being attacked by a civilian constitutes just cause; however, it is dishonorable to goad a civilian into attacking a trained warrior.
- It is honorable to care for your comrades, your weapon and your mounts before yourself, for they are your succor in battle. It is dishonorable to neglect your comrades in the field, the food and care of the troops you lead or of prisoners in battle.
- Mutual truces are sacred. To violate the terms of a truce is blackest dishonor, and he who does so shall find that Lord Upuaut has turned His face away from him. If ending a truce is necessary, it is dishonorable not to inform the enemy commander beforehand. Heralds or emissaries must be given time to return to their lines, and if this is not possible they must be treated as honored guests, not as prisoners.
- The use of sorcery in battle, as with any other skill, is not dishonorable. The use of necromancy is highly dishonorable, and its use in the field is just cause for the voiding of the nikobi.
- When captured in battle, it is not dishonorable to attempt to escape or to damage the foe in any way possible. It is dishonorable to slay a recaptured escapee. However, any escapee who breaks the law or slays his captors may be honorably dealt with as the laws require. If parole is given, it is dishonorable for the parolee to try to escape.
- To disobey orders to perform dishonorable tasks is honorable. It is dishonorable to do so without informing your commander why you are disobeying orders and without standing fast - if possible- to allow him to countermand. If the commander knowingly persists in the ways of dishonor, the nikobi must be voided, for only a coward or a bandit remains under the charge of a dishonorable leader. If there is dissension, the paktunsa must vote on the matter, a majority carrying.
- However, a mercenary’s conscience is his own, and to Lord Upuaut be the judgment. It is honorable to convince a comrade to turn from the path of dishonor, but dishonorable to force him to do so.
- Honor and respect the paktunsa, for such warriors are blessed of the Lord Upuaut. In return, a paktun’s actions and bearing must be worthy of respect, for he serves as an example to the host. The paktun who acts in dishonor blackens the name of his host and his god; if he not repent of his evil, let him suffer just and sudden death.
- The blessing of the Lord Upuaut are upon the honorable mercenary, but His curse rests on he who acts with dishonor.
There's a great deal of debate on those points; you can see where the Code has loopholes and conflicting sections. Mercenary rapists have tried to argue, for instance, that their victims weren't "harmed" – there ain't no blood, is there?
On the more liberal side of things, there's a faction that holds that looting "too much" harms the victims.
There's certainly plenty of fodder for barracks lawyers and litigants back in the cities; on the latter count, some of the nations are extending a concept akin to sovereign immunity on mercenary companies under their hire, pretty much solely to ensure that they can hire companies for the next campaigning season.
When all is said and done, of course, there are companies which skirt as close to the line as possible, the operating principle being "how much can we get away with before the paktunsa vote to take us out?"