Complex sentence: Another battle is that of the Silent Pools, or Twilight Pools which is Umboth Muilin or Ailin Uial to which it is suggested that the Easterling Men of Hithlum descend from the north and the flank of the Elves.
Split into simpler sentences: Another battle is that of the Silent Pools, or Twilight Pools which is Umboth Muilin, or Ailin Uial. Here it is suggested that the Easterling Men of Hithlum descend from the north and attack the flank of the Elves.