As the Antichrist attempts to kill all Jews, then adding Christians to the list also, he finally requires every person in the world to worship his image and receive his name or number on their hand or forehead or be killed. God then sends angels to pour out His plagues on all those having the mark of the beast.

Rev 16:2 “So the first went and poured out his bowl upon the earth, and a foul and loathsome sore came upon the men who had the mark of the beast and those who worshiped his image.”

Satan realizes that the Second Coming of Christ is nearing so he deceives all the kings and armies of the entire world into gathering without telling them the real purpose of their gathering. They think they are going to unseat Antichrist and each one hopes to gain the supremacy, unaware that in reality they would be faced with Christ, the King of Kings and Lord of Lords.

Rev 16:13, 14, 16 “And I saw three unclean spirits like frogs [coming] out of the mouth of the dragon, out of the mouth of the beast, and out of the mouth of the false prophet. For they are spirits of demons, performing signs, [which] go out to the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.
Rev 16:16 And he gathered them together into a place called in the Hebrew tongue Armageddon.”

The valley of Meggido is a huge, flat open area where many historic wars have been fought and is bordered on the north by a strategic mountain pass vital to the protection of Israel from armies from the north.

Once gathered, the armies of the nations of the world forget about their personal ambitions and join together to fight against Christ, their common enemy who comes upon them by surprise.

Rev 19:11-13 “Now I saw heaven opened, and behold, a white horse. And He who sat on him [was] called Faithful and True, and in righteousness He judges and makes war. He [was] clothed with a robe dipped in blood, and His name is called The Word of God.
John 1:1 In the beginning was the Word, and the Word was with God, and the Word was God.”
Rev 19:14 And the armies [which were] in heaven followed him upon white horses, clothed in fine linen, white and clean.
Zec 14:4 “And in that day His feet will stand on the Mount of Olives,”
Zec 12:9 “It shall be in that day [that] I will seek to destroy all the nations that come against Jerusalem.”
Rev 19:19 And I saw the beast, the kings of the earth, and their armies, gathered together to make war against Him who sat on the horse and against His army.
Rev 19:15 Now out of His mouth goes a sharp sword, that with it He should strike the nations.

Christ will speak and all the gathered armies of the world die. His army that accompanies Him will be present watching the victory but will not need to fight. The battle is over, the saints are present, but just watching. The bodies of hundreds of millions of unbelieving soldiers, from every nation on earth fill the valley of Megiddo. This will doubtless be the shortest battle every waged. Satan lost the battle, but since one of his goals is to fill hell, he will no doubt enjoy some degree of satisfaction.

The cleanup process must now begin. An angel invites scavenger birds to come to the supper of the great God.

Rev 19:17,18 “Then I saw an angel standing in the sun; and he cried with a loud voice, saying to all the birds that fly in the midst of heaven, ‘Come and gather together for the supper of the great God, that you may eat the flesh of kings, the flesh of captains, the flesh of mighty men, the flesh of horses and of those who sit on them, and the flesh of all [people], free and slave, both small and great.’ "

Meanwhile, Israel will receive their true Messiah.
Zec 12:10 "And I will pour on the house of David and on the inhabitants of Jerusalem the Spirit of grace and supplication; then they will look on Me whom they pierced. Yes, they will mourn for Him as one mourns for [his] only [son], and grieve for Him as one grieves for a firstborn.”

Christ will judge the nations. Goats (unbelievers) will go to the lake of fire and sheep (believers) enter the millennium to reign with Christ for one thousand years.

Matt 25:46 “And these will go away into everlasting punishment, but the righteous into life eternal.”

What can we learn from the battle of Armageddon where the largest army ever amassed was conquered by just a word from God? Moses gives us the answer in Exodus 14:13-14.

“And Moses said unto the people, Fear not, stand still, and see the salvation of the LORD, which he will show you today: for the Egyptians whom you have seen today, you shall see them again no more forever. The LORD shall fight for you, and ye shall hold your peace.”

When am I going to learn to trust God for my impossible battles, crying out to Him for help and seeing Him work?