The end of the Third Age is a time where good and evil wage a decisive war for the final domination of Middle-earth.
Both ways, freeing the good people of Middle earth as well as bringing the world under the shadow will not be an easy task for the player.
A new campaign and battle AI will make life much harder and a unit recruitment based on a cultural level and a regional recruitment requires strategically decisions and will slow down your expansion if not properly planned.
The AI will also receive certain bonuses like extra money or additional armies if they get in serious trouble to compensate the lack of human intelligence and the lack of income through missions.