This is the huge battle for Middle Earth, which is in the new Lord of the Rings film, the Return of the King. I based it on what clips I saw of the trailer and what I read in the book, so if anything is wrong, could you please send me some info on what's wrong and I will fix it. :)
Enemy to win - kill everyone, if you kill Frodo Mordor will become extremely powerful and will probably win,
Good guys to win - defend Minas Tirith, if you get to Mount Doom with Frodo Mordor will fall. If you kill the winged Nazgul, the forces of Middle Earth will lose power