The Mercenaries of the Iron Kingdoms conduct war as a trade in an open market. Primarily making their homes to the north of Cygnar in the small kingdom of Ord, Mercenaries are a facet of everyday life in Western Immoren. A code as old as the Iron Kingdoms themselves rules their conduct, and in many cases these bands of sell-swords are more forthright in their dealings than most victuals merchants. Violating this ancient Charter is a grave act which will ruin a Mercenary company for many reasons - the foremost of which is the reality that the Charter is accepted as law in almost all of the Iron Kingdoms
Mercenaries in good standing are accept contracts to conduct military action against other military forces. Some of these contracts are from private individuals, but the main employers of Mercenary companies are the Iron Kingdoms themselves. It's sometimes humorous to review a company's deployment history - though they never accept missions against the agency that first commissioned them, they very often fight against those they recently were employed by. Unless of course that particular contract stipulated a "cooling down" period against the employer.
There are four big contracts that constantly attract new companies. These are for major military forces, for the most part. For example, the Highborn Covenant Contract is pretty much given to any Mercenary company who is fighting in occupied Llael, especially if they are hired by the Cygnaran government or the Llaelese government in-exile. The Searforge Commission is a contract that any potential mercenary commander has to deal with if they want to hire Rhulic mercenaries. However, the Four-Star Syndicate has a standard contract, and routinely hires companies of Mercenaries to conduct its more brazen raids. Even the fleets of pirates on the Broken Coast have founded their own standard contract, called the Talion Charter.
In our particular neck of the woods, there are large movements of the Steelheads, an old and highly reputable Mercenary company. Aside from a few smaller companies of great renown, it's this company you're most likely to encounter. The Steelheads are very large, and have multiple deployments across a wide range of contracts - of course, they never violate the Mercenary Charter by creating a "conflict of interests". However, there are whispers of soldiers marching out of Rhul...
The bottom line is that Mercenaries are employed as a matter of course by the military powers of the Iron Kingdoms. They are motivated solely by profit, and governed by honor. Non-military targets are never accepted, and civilians are never tortured, pillaged or extorted. This is ancient tradition, and practical policy as well. In many cases, Mercenary companies behave better than many national militaries. It is for this reason the populace at large does not balk at such private armies.
Many laws, contracts and charters rule the Mercenary's life. Yet, this code has a certain honor in it. Many commanders never feel restrained by it at all, but rather they feel liberated from many other laws. Though there are many strictures in the Charter, a clever Mercenary commander can find a lot of wiggle-room in the wording of his contracts.