The Battle of Armageddon
"And the sixth angel poured out his vial upon the great river Euphrates; and the water thereof was dried up, that the way of the kings of the east might be prepared. And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet. For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty. Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame. And he gathered them together into a place called in the Hebrew tongue Armageddon." (Revelation 16:12-26 KJV)
"Then shall The Lord go forth, and fight against those nations"
The "battle of Armageddon" or just "Armageddon" is a popular "doomsday" term (see also The End Of The World?). While many claim to use it based on the Bible, the use of "Armageddon" very often ignores what the Bible itself plainly says about it. Firstly, the plains of Armageddon are where a great mass of armies will gather, not fight. Secondly, "Armageddon" is not about a great war between nations. It's about the nations of the world fighting Christ at His return.
"And he gathered them together into a place called in the Hebrew tongue Armageddon" is followed by a great battle that The Lord will fight with the nations at His return to the Mount of Olives:
"And I saw heaven opened, and behold a white horse; and He that sat upon him was called Faithful and True, and in righteousness He doth judge and make war." [see also Valley of Jehoshaphat]
"His eyes were as a flame of fire, and on His head were many crowns; and He had a name written, that no man knew, but He Himself. And He was clothed with a vesture dipped in blood: and His name is called The Word of God." [see The Logos]
"And the armies which were in heaven followed Him upon white horses, clothed in fine linen, white and clean. And out of His mouth goeth a sharp sword, that with it he should smite the nations: and He shall rule them with a rod of iron [see also The Coming World Dictator]: and He treadeth the winepress of the fierceness and wrath of Almighty God." (Revelation 19:11-15 KJV)
"Then shall The Lord go forth, and fight against those nations, as when He fought in the day of battle. And His feet shall stand in that day upon The Mount Of Olives, which is before Jerusalem on the east, and the mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley; and half of the mountain shall remove toward the north, and half of it toward the south." (Zechariah 14:3-4 KJV)
Fact Finder: What two prophets of God will be martyred in Jerusalem just before Christ's return?
See Smoke On The Water, Fire In The Sky, also Sodom and Egypt and How Does The Ark Get To Heaven?