How will the Russian/northern army be defeated and destroyed?
The northern army will be defeated by its own confusion—every man's sword against his brother—and by God's direct intervention: pestilence, blood, hailstones, fire, and brimstone. God will turn them back, leaving only a sixth part, and they will be utterly destroyed on the hills and mountains of Israel.
Les explains that this northern army, often identified as Russian, will be defeated not only by its own confusion—where every man's sword turns against his brother, causing them to annihilate themselves—but also by God's tremendous power. Les compares this to the red horse statement in Revelation and to Sodom and Gomorrah, as God rains pestilence, blood, hailstones, fire, and brimstone upon them. God will magnify and sanctify Himself, making Himself known to many nations. In Ezekiel 39, God says He is against Gog, will turn them back, leave only a sixth part, and bring them to the mountains of Israel, where He will smite the bow from their left hand and cause arrows to fall from their right. They will be utterly destroyed on Israel's hills and mountains.