The Retribution is an extremist paramilitary organization that grows increasingly influential in the secluded elvish nation of Ios. For reasons not fully understood, the Iosan gods are all dead or dying which is causing Iosan children to be born without souls, putting their race on the brink of extinction (as seems typical of elves in all fantasy worlds). The Retribution believes the cause of their dilemma is the use of magic by humans, and have decided the best solution is to kill every human arcanist. Given that the Iron Kingdoms are populated with thousands of humans with arcane ability of some degree, this is a hopeless task.
So far, the other nations are largely unaware or unconcerned with the Retribution's activities, so you might say they have been hugely unsuccessful in their stated purpose. In recent years the Skorne have mounted a large invasion onto Iosan lands and this has preoccupied the Retribution and the main Ios military. On the other hand, the conflict has resulted in much more of the military coming under the banner of the Retribution, vastly increasing their options.