This battle will be a great war like has never been seen on the face of the earth. The seventh vial describes the actual war in great detail.
And there were voices, and thunders, and lightnings; and there was a great earthquake, such as was not since men were upon the earth, so mighty an earthquake, and so great. And the great city was divided into three parts…
That is the city of Babylon representing the anti-Christian kingdom.
…and the cities of the nations fell: and great Babylon came in remembrance before God, to give unto her the cup of the wine of the fierceness of his wrath. And every island fled away, and the mountains were not found. And there fell upon men a great hail out of heaven, every stone about the weight of a talent: and men blasphemed God because of the plague of the hail; for the plague thereof was exceeding great. Revelation 16:18–21, KJV
God is unleashing His wrath upon this kingdom of men in the middle of this war. There is a lightning and thunder. There is great hail falling out of the sky in the midst of this battle. There is an earthquake larger than any earthquake that has ever been in the history of the world, which occurs right in the midst of this great worldwide civil war. Cities and buildings are coming crashing down as this war is going on. God gives the wicked world that opposed Him the cup of the wine of the fierceness of His wrath, the text says. Picture in your mind all the power of modern warfare being unleashed, as the whole world erupts into civil war – atomic bombs, missiles, jet fighters. In the midst of the turmoil of great war, there is the greatest earthquake that the world has ever known, and hail and thunder. Man is himself destroying himself. And God joins in in the destruction of man's great depraved kingdom, so that man might see the end of himself apart from God and His covenant.1
Cory Griess
18 And there were flashes of lightning, rumblings, peals of thunder, and a great earthquake such as there had never been since man was on the earth, so great was that earthquake.