We all know that during the era of Lord of the Rings, "one does not simply walk into Mordor," but there was a time when the land of orcs and goblins wasn't an evil fortress. In the years after Sauron fell, humans actually took back small parts of Mordor, setting up camps and reclaiming the dark world for their own. Eventually, though, Sauron returns, bringing with him enough orcs to kick out the remaining humans--that, exactly, is when the game begins.
Where does it go from there? How does it tie into the lore? We don't know, but concept art reveals something interesting. It appears that, in one image, Talion is wielding the shattered sword Narsil, the weapon Isildor used to defeat Sauron and would later be reforged as Andúril for Aragorn. Why does he have it? Where does he get it? How many fetch quests does it take to go collect all the broken pieces scattered around Mordor? We don't know just yet.