Not only has relations between Rohan and the Reunited Kingdom become strained, but thanks to said strife several emergent factions of men have risen up, and the Chiefdoms of Dunland, Rhûn and the Empire of Harad have gone on the offensive. In this setting the Reunited Kingdom of Gondor and Arnor has become badly weakened by political strife amongst Aragorn's descendants, resulting in half the kingdom splintering and forming the Kingdom of Adûnabâr in Mordor, Angmar and Ithilien, with rumors that a dark cult is behind this civil war.
A case of justified Gameplay and Story Segregation changes a few of the ideas that were in the unfinished tale due to the developers using their imaginations, this manages to create a realistic and true setting within Tolkien's work. However Tolkien abandoned this after only a few pages without providing additional backstory or characters. It is based off Tolkien's unfinished manuscript (of the same name) for a sequel to The Lord of the Rings where Eldarion, the son of Aragorn Elessar and king of the Reunited Kingdom, has to deal with his people turning to evil practices in the lands of Gondor.
The current version of the mod is known as The Dominion of Men, the sequel to version 2.6 " The New Shadow".