With a growing user base, the massively multiplayer online game based on J.R.R. Tolkien’s world of Middle-earth continues to aim to become the one game to rule them all. On Friday, Boston-based developer Turbine Inc. announced a new expansion pack for The Lord of the Rings Online Gold this fall. Following last year retail expansion Mines of Moria, Siege of Mirkwood will complete Volume II of the storyline in the Lord of the Rings Online universe. In the new expansion, players will band together eastward towards the perilous forest of Mirkwood.