How will the Russian or northern army be defeated in Ezekiel 38–39?
The Russian or northern army will be defeated by internal confusion—every man's sword against his brother—and by God's direct power: pestilence, blood, hailstones, fire, and brimstone, like Sodom and Gomorrah. God will utterly destroy them on Israel's mountains, turn them back, and leave only a sixth part.
Les explains that Ezekiel's prophecy compares with Revelation's red horse statement: every man's sword will be against his brother, meaning they will be annihilating themselves. God also comes in with His own power, pleading against him with pestilence and blood, and raining upon him and his bands an overflowing rain of great hailstones, fire, and brimstone—the same language as Sodom and Gomorrah. Thus the Russian or northern army will be defeated not only by its own confusion but by a tremendous power of God, utterly destroyed on the hills and mountains of Israel. In chapter 39, God says He is against Gog, will turn him back, leave but the sixth part, cause him to come up from the north parts, and bring him on the mountains of Israel. God will smite the bow out of the left hand and cause the arrows to fall out of the right. This is how God deals with nations when He judges them: He brought them into Israel, destroyed them there, and turns them back.