The war is about and over the souls of men. That is what the Bible, the Gospel, the Incarnation and the Cross are all about.
Part of the war took place in Heaven. “There was war in heaven. Michael and his angels fought against the dragon. And the dragon and his angels fought back. But the dragon wasn’t strong enough. He and his angels lost their place in heaven. The great dragon was thrown down to the earth and his angels with him. The dragon is that old serpent called the devil, or Satan. He leads the whole world down the wrong path” (Rev. 12: 7-9).
The rest of the war takes place on earth.
Then I heard a loud voice in heaven. It said, “Now the salvation and the power and the kingdom of our God have come. The authority of his Christ has come. Satan, who brings charges against our brothers and sisters, has been thrown down. He brings charges against them before our God day and night. They overcame him because the Lamb gave his life’s blood for them. They overcame him by giving witness about Jesus to others. They were willing to risk their lives, even if it led to death. So be joyful, you heavens! Be glad, all you who live there! But how terrible it will be for the earth and the sea! The devil has come down to you. He is very angry. He knows his time is short.” (Rev. 12:10-12)