Why Har-Magedon? There was, we have every reason to believe, no such place. The name is symbolical. It is a compound word derived from the Hebrew, and signifying the mountain of Megiddo. We are thus again taken back to Old Testament history, in which the great plain of Megiddo, the most extensive in Palestine, plays on more than one occasion a notable part. In particular, that plain was famous for two great slaughters, that of the Canaanitish host by Barak, celebrated in the song of Deborah, and that in which King Josiah fell. The former is probably alluded to, for the enemies of Israel were there completely routed. For a similar though still more terrible destruction the hosts of evil are assembled at Har-Magedon. The Seer thinks it enough to assemble them, and to name the place. He does not need to go further or to describe the victory.Milligan, William. The Expositor's Bible: The Book of Revelation (Kindle Locations 3649-3651). Kindle Edition.
Milligan, William. The Expositor's Bible: The Book of Revelation (Kindle Locations 3644-3649). Kindle Edition.
Milligan, William. The Expositor's Bible: The Book of Revelation (Kindle Location 3644). Kindle Edition.
Note: For you spelling purists out there, the word may be spelled "Har-Magedon," Harmagedon or Harmageddon. Also see the more recent paper written here: http://home.tamk.fi/~mark/fi/docs/Armageddon.pdf