Ezekiel - Chapter 38
Gog and Magog
G-d told Ezekiel to face the direction of Gog, king of Magog, and speak of his future. G-d opposes Gog, whom He will lead out along with his great army. Many other nations, including Persia, Ethiopia and Togarmah (which might be Germany), will join Gog and his forces. Gog should prepare himself for the battle to come. His forces will march upon the exiles who have returned to Israel. Gog and Magog (and their allies) will ascend to assault Israel, covering it like a fog. They will plan evil - to oppose G-d and to attack innocent people in undefended cities, to loot and pillage the resettled exiles. Merchants of trading lands stand ready to buy the plundered wealth of Israel.
But... when Gog and his allies attack Israel, it will be "the end of days." It's "Judgment Day" for all the nations. People will know that Gog is the one G-d foretold through two prophets (presumably Ezekiel and Zechariah, although the Talmud in Sanhedrin, page 17a, says that it was Eldad and Medad, who prophesied in Numbers chapter 11). When Gog and Magog attack, G-d will remember their sins and direct His wrath against them. All the fish in the sea, the birds in the sky, the beasts in the field and people on the Earth will tremble and mountains will fall. Everyone in the massive army will attack one another in the great confusion. Plague, blood, floods, hail, fire and sulfur will rain down on Gog's forces. The nations will observe this and recognize G-d's greatness.
People are used to hearing of the "war of Gog and Magog" and they mistakenly think that Gog and Magog are two opposing nations. They're not. Magog is the nation, descended from Noah's son Japheth, and Gog is their leader. (It's like people thinking that the French fought Indians in the "French and Indian War" - really, the British fought France, who had Native American allies. The name is misleading.)