Armageddon, (probably Hebrew: “Hill of Megiddo”), in the New Testament, place where the kings of the Earth under demonic leadership will wage war on the forces of God at the end of history. Armageddon is mentioned in the Bible only once, in the Revelation to John, or the Apocalypse of St. John (16:16).
Now follows here some details of the terrible physical Judgements on the peoples of the Nations on Earth, who had and will cause to be rejected, derided and persecuted the people of God prior to Christ's Second Advent; the Jews, and Christians prior to Revelation, and the Ecclesia and Overcomers of Revelation. The details are so horrific in human terms, that in verses 5 and 6, clear justification of God's actions are proclaimed by a loyal angel! It is clear that Almighty God is deeply affected by what He is instigating here, and as The Only Righteous One, His feelings for His Creation, despite its depravity, is deep beyond our ability to fathom! This makes sense and chimes with verse 8 of Chapter 15.
V.16 And (a)He/they gathered them together into a place called in the Hebrew tongue (b)Armageddon.
(a) “He”; the 1611 translators for C. of E. again in error. This “he”: should be translated “they”, so also the NKJV. The reference is to V.14, the demons, the purpose is the gathering together of the Nations to war/annihilate the people of Israel at 'Har-mageddon' (Armageddon).
As a note of interest, AV gives "he", Darby "he", NIV "they", Youngs Literal "they", Moffatt "they were mustered" (referring to the Nations), Interlinear "He", NKJV "they".
(b) “Armageddon”; (Har-Megeddon), this word means “mount of Megiddo”, (Comp. page 1905). See Judges 5:19 & Isa. 10:28. It is located in the YEZREEL VALLEY. It has been a battlefield between Kingdoms for more than 4000 years B.C.! It is mentioned in various Ancient writings including the Pharaoh Thutmose the third (1500 B.C.). The king of Megiddo was one of the kings defeated by Joshua (Josh. 12:21). The city of Megiddo did not become of the tribal allotments until King David.
General Allenby fought and won a battle with the Turks there, in the first World War (Ottoman Empire) and received the title of “Lord of Megiddo” for that victory. It lies approx. 70 miles due north of Jerusalem!
See: Rev Chapter 16