The options are:
The dragon was so frustrated with not being able to devour the child (Revelation 12:5) that he followed the child into heaven in an attempt still to devour him—and now Michael seeks to repel him. However, the text nowhere tells us that the dragon stormed heaven in an effort to devour the child; the thought is speculation. Furthermore, we are not to picture the dragon invading heaven because the sign itself appeared in heaven in the first place (Revelation 12:3).
The reference to the child being “caught up to God” encapsulates Jesus’ victory on the cross (Colossians 2:15). Satan’s defeat at the cross implies that he of necessity must be exiled from Christ’s throne room (Ephesians 1:20–22). So, “war arose in heaven,” with godly angels seeking to expel Satan from heaven.
7 Now war arose in heaven, Michael and his angels fighting against the dragon. And the dragon and his angels fought back,