Why will the northern/Russian army be defeated in the invasion of Israel?
The northern/Russian army will be defeated by its own internal confusion—every man's sword against his brother—and by the direct, overwhelming power of God. God will bring pestilence, blood, hailstones, fire, and brimstone upon them, utterly destroying them on Israel's hills and mountains, magnifying Himself before the nations.
Les explains that the northern/Russian army will be defeated in two ways. First, there will be internal confusion: every man's sword will be against his brother, so they annihilate themselves. Second, God will come in with His own power, pleading against Gog with pestilence and blood, and raining upon him and his bands an overflowing rain of great hailstones, fire, and brimstone—the same language used of Sodom and Gomorrah. God says He will magnify and sanctify Himself and be known in the eyes of many nations, and they shall know that He is the Lord. God also tells Gog He is against him, will turn him back, leave but a sixth part, bring him up on the mountains of Israel, smite the bow out of his left hand, and cause his arrows to fall from his right. The army is utterly destroyed on the hills and mountains of Israel.
And I will call for a sword against him throughout all my mountains, saith the Lord GOD: every man’s sword shall be against his brother.
And I will plead against him with pestilence and with blood; and I will rain upon him, and upon his bands, and upon the many people that are with him, an overflowing rain, and great hailstones, fire, and brimstone.