That is, the spirits of demons (Rev. Rev. 16:13+) gathered the kings of the earth (Rev. Rev. 16:14+).
to the place called in Hebrew, Armageddon
Ἁρμαγεδών [Harmagedōn] : A Hebrew place-name meaning Mount or Hill of Megiddo and generally identified as the fortress overlooking a pass through the Carmel Range into Galilee.1 From a combination of Hebrew הָר [hār] , mountain, and מְגִדּוֹן [meḡiddôn] (Zec. Zec. 12:11), Megiddo. Megiddo probably means a place of troops (from גַד [ḡaḏ] ), a troop (Gen. Gen. 49:19); and the verb גָדַד [ḡāḏaḏ] ), to cut to pieces.2 Strong gives the meaning as place of crowds.3
Some find a reference to the hill country near Megiddo unconvincing and look for an alternative understanding:
Har-Magedon would mean the Mountain of Megiddo, but here a difficulty arises: there is no Mount Megiddo. None of the solutions offered is especially persuasive. It is possible that Har-Magedon could be a reference to the hill country near Megiddo or perhaps a reference to Megiddo and Mount Carmel in the same breath (Farrer, p. 178). In Johns day the tell or mount upon which Megiddo was built was about seventy feet in height, hardly enough to justify the designation Mount. One frequent suggestion is that the Apocalyptist began with Ezekiels prophecy of a great eschatological slaughter of the nations on the mountains of Israel (Eze. Eze. 38:8-21; Eze. 39:2, Eze. 39:4, Eze. 39:17) and then made the reference more specific by adding the name Megiddo as the place where so often in Israels history the enemies of God were destroyed (Beckwith, p. 685). Still others interpret the term in reference to some ancient myth in which an army of demons assault the holy mountain of the gods. If one reads Armageddon (instead of Har-Magedon), the reference could be to the city of Megiddo rather than to a mountain. Others interpret Har-Magedon without reference to Megiddo. Bruce (p. 657), following C. C. Torrey, mentions har mōʿēd , the mount of assembly (Isa. Isa. 14:13). Or it could be a corruption in the Hebrew text for his fruitful mountain or the desirable city (i.e. , Jerusalem). . . . Yet another suggestion is that Megiddo could be derived from a root meaning to cut, attack, or maraud. In this case Mount Megiddo would mean the marauding mountain (a variant to Jeremiahs destroying mountain, Jer. Jer. 51:25) and indicate that John expected the battle not in northern Palestine but at Rome [Mounce takes Babylon to be Rome] (Caird, p. 207; cf. Kiddle, pp. 329-31). As in the case of the number of the beast (Rev. Rev. 13:18+), the cryptic nature of the reference has thus far defeated all attempts at a final answer.6It is our view that the phrase probably denotes the hill country near Megiddo, at the edge of the Jezreel Valley which is an optimum place to access the Promised Land by sea and to serve as a staging area for vast armies. The drying up of the Euphrates river, a real geographical location, so that kings from the east can be gathered to Armageddon argues that Armageddon itself is a real geographical location west of the Euphrates rather than to be taken as a spiritual concept. See Megiddo
5 John MacArthur, Revelation 12-22 : The MacArthur New Testament Commentary (Chicago, IL: Moody Press, 2000), Rev. 16:18.