Rohan perhaps boasts the greatest continuity from TNS to DoM. It's only sensible: after all, Rohan claims no lands in the North, and no new factions have cropped up on its borders. With the exception of some new or altered provinces in the periphery of its lands, the starting situation of Rohan will be familiar to players of TNS.
In terms of units, too, those who loved playing the horse-lords in TNS will find their DoM incarnation largely unchanged. Yes, you'll still be able to enjoy lining up your cavalry and plowing through hordes of hapless Dunlendings in a thunderous charge. And though it probably doesn't get as much attention,Rohan's infantry is still a solid force of spearmen and axemen, able to hold a battle line while your riders flank or to assault or defend during a siege.
All of the above means Rohan is a great choice for players to get their feet wet in the ocean of new features introduced by DoM. But what is different this time around?
While the early game will likely play out the same as it did in TNS, Dunland may have some more longevity in DoM. If the Dunlendings manage to push across the Greyflood and threaten the lands of Arnor, they will be harder to defeat decisively. Dunland has some more elbow-room in the North – don't be surprised if they use it.
And conquering Dunland no longer provides Rohan with a safe corner, necessarily. True, your ally the Reunited Kingdom holds lands in the North, but if you crush Dunland early on, the City-kingdom of Tharbad may still have a strong presence along the Greyflood. Tharbad may have helped you defeat the Dunlendings, or may have turned north and found trouble with the Reunited Kingdom. Either way, Tharbad is a faction to be wary of. Surrounded by powerful neighbors, it may strike out
The eastern border is more lively. Beyond Fangorn is the forest of
Lorien, the nearest Elven outpost to your lands. The Elves are often quiet neighbors, unwilling to involve themselves with the troubles of the world of Men, but sometimes disputes erupt.
More troubling is the Kingdom of Adunabar, which holds land across the Anduin and may push its way north toward Greenwood. A powerful Adunabar,with its strong Dunedanic soldiers, can be a challenging foe – all the more reason, then, to aid the RK in its battles around Osgiliath and Ithilien, or to cross at the Undeeps and harry the enemy in the Brown Lands.
The lands about the southern Greenwood and Rhovanion can change hands frequently, since many factions vie for them. The Beornings in the Valesof Anduin, the Men of Rhovanion or of Dale, and the Easterlings of Rhunmay all enter the fray, as allies, enemies, or (temporarily) neutral powers. Note the presence of several Northmen factions in the area. They may all share a culture and generally follow the Ways of the West, but conflict among Northmen is nothing new, with some peoples of Rhovanion even siding with Easterlings for the pursuit of their own feuds in the distant past of the Third Age. The Age of Men is a time of changing loyalties – something a wise king of Rohan must remember as he extends his people's realm and defeats old foes.
Fortunately, Rohan's alliance with the Reunited Kingdom is not so susceptible to that change. The 'perpetual alliance' mentioned in tales of Cirion and Eorl holds into the Fourth Age, giving Rohan a rare position of strength. With a strong and secure trade partner in its ally, Rohan can grow wealthy enough to afford to send armies to its aid -north, east, or south. And if south, those armies may pass the barrow of Folcred and Fastred above the Poros, twin sons of Rohan whose very lives fulfilled the great Oath of their forefathers.