One of Age of the Ring's primary goals is to create a fun and engaging RTS that is as faithful to Tolkien's stories as possible.
What this means can vary between factions and the reality of what an RTS game requires. We can't always achieve this through strict adherence to Tolkien's text and the things mentioned in it: a faction such as Dol Guldur or Haradwaith cannot exist if all its content were directly sourced from Tolkien.
In these cases we create new characters and locations that fit the themes, mood, and physical reality of Middle-earth as closely as possible. We are careful not to write anything that invalidates or contradicts anything written by Tolkien. We consider these original creations part of the Age of the Ring Canon, and treat them with the same care and attention as we do the creations of Tolkien himself, in order to make them blend as seamlessly as possible. Some parts of the Age of the Ring Canon (names, especially) were inspired by other sources such as LotR video games or Games Workshop's LotR miniatures, but each of these instances were provided with new, original background lore.
There are many instances of characters in Age of the Ring that were not directly mentioned by Tolkien, but are not part of AotR Canon. The distinction here is that these characters (most often units) can be very easily extrapolated from Tolkien's text, or whose existence within it is self-explanatory and didn't require Tolkien's specific mention. Linhir Spearmen are good examples of this: Tolkien does not directly mention them, but their presence in Age of the Ring does not meet the requirements of being a wholly original creation. Conversely, Bree-land Townsguard do belong in AotR Canon, as Tolkien makes no mention, implication, or approximation of any sort of militarization within the Bree-lands, but stops short of ruling it out completely.
A growing compendium of AotR Canon creations can be found below.
AotR Canon Compendium Edit
In addition to the above listed, many key events in AOTR Canon are portrayed somewhat uniquely within the mod, most noticeably with regards to the Lord of the Rings Campaign. The campaign missions combine elements of both the books and movies, with unique elements and plotlines that are not present in either.
Shadow of the Past
Gildor and his elves launch an assault on the Barrow-Downs themselves with Tom Bombadil's aid after being attacked by Undead Dunedain, fighting off hordes of undead and even the Nazgul themselves. In addition, the Nazgul attack Bree with hordes of these same undead while Aragorn and the Hobbits muster forces of Hobbits and Breelanders to fight them off, while in the original canon the Nazgul attacked Bree alone with little resistance.
Fords of the Bruinen
When Glorfindel finds the Fellowship and Frodo crippled by the Morgul Blade, he sends Frodo alone on Asfaloth to safety at Rivendell. The Nazgul, after confronting Arwen at the river Bruinen, unleashes hordes of Orcs, Undead, Wolves and even Castellans of Dol Guldur, as Arwen and battalions of Rivendell Elves hold the line against them. Glorfindel, Aragorn, and the remaining Hobbits arrive at the River while the battle is raging and choose to join the battle once they reach the safety of Rivendell's elves. In the book and film, the Nazgul themselves chased Frodo, who rode alongside Glorfindel in the book and Arwen in the film, and no large-scale battle at the Bruinen took place.
A Journey in the Dark
When the Fellowship discover the account of Balin's expedition in Moria (which is then made playable), both Balin and Oin are both still alive when Moria is invaded by Goblins and Gundabad Orcs, although the Dwarves are trapped and their fate is increasingly grim. Neither Dwarven hero was alive by this time in the book, in which Balin was killed by an orc arrow before the orcs invaded Moria to recapture it, while Oin was killed by the Watcher in the Water while trying to find an escape out through the West Gate.
The Woods of Lothlorien
Lothlorien is attacked by a large horde of Goblins after the Fellowship reach safety, led by the shaman Urshak. No such attack occurred in either the book or film.
Breaking of the Fellowship
In the original canon, Boromir was killed at Amon Hen by multiple Uruk-hai and Lurtz in the books and films, respectively. However, in AOTR canon, Boromir can be saved if Aragorn reaches him in time and keeps him alive throughout the fight with Lurtz.