The battle of Armageddon will be fought when Jesus returns to earth at the end of Great Tribulation. The saints will follow Him back to earth as part of the armies of Heaven, clothed with righteousness. The entire world will be drawn into this great conflict by demonic spirits that come forth from the Antichrist himself.
Jesus wins the battle by speaking the Word of God. He will capture the Antichrist and his false prophet and cast them into the lake of fire. The remainder of his followers will be put to death by the sword coming from His mouth. After this, the Millennial reign of Christ begins on the earth.
Key Scriptures: Revelation 16:12-16, Revelation 19:11-21, 1 John 3:3