War in Heaven means in the bible: The Rev. This term refers to conflict which took place during the premortal existence of the spirit children. It was about how the salvation plan would be implemented to the future human family. These issues included agency and how to get salvation. One-third of all the spirits rejected Jesus Christ’s appointment as their Savior. This refusal was rebellion against God’s plan for redemption. Lucifer wanted to see salvation come to everyone who lived through death, regardless of individual preferences, agency or voluntariness. 14:12-20, Luke 10:18-18; Rev. 12:4-13, DC 29:36-40; Moses 4:4-4. The rebellious spirits that persisted in their rebellion were thrown out of heaven, and sent down to earth with no mortal bodies. DC 29:37. See also Rev. 12:9; Abr. 3:24-28.
(in Bible Dictionary)