Armageddon (Hill of Megiddo in Hebrew) refers to the gathering place of the world’s armies in their final battle against Israel.
This battle will conclude with Christ’s return, as He Himself will save Israel. This is known as the second coming of Christ and will usher in the new Millennium Kingdom.
“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. 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. 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: and he treadeth the winepress of the fierceness and wrath of Almighty God. And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS.”
REVELATION 19:11-16 (KJV, HOLY BIBLE)