War in Heaven
The War in Heaven is the conflict that took place in the premortal life among the spirit children of God. The Book of Revelation states,
- And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels,
- And prevailed not; neither was their place found any more in heaven.
- And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him (Revelation 12: 4, 7-9).
Time line of the War in Heaven
The extensive nature of the council in Heaven suggests that it was ongoing. Also, the term council does not necessarily refer to a one time event but could also refer to an organization. In other words, the council in heaven could refer to a one time event, or to a group of individuals counseling together.
Lucifer was a participant in the council in heaven. He was considered a "Son of the Morning" and was "in authority in the presence of God" prior to his fall. As the plan of salvation was presented in the council in heaven, God explained that there would be a need for someone to enable God's children to return to Him from the earthly experience. All of God's children would sin during their sojourn on earth, and Adam's predicted fall would result in both physical and spiritual death, from which God's children would need to be redeemed.
God's plan "from the beginning" was to rely on Jehovah (Christ). However, at some point God sought the common consent of His spirit children, as to who would be sent to earth. Lucifer presented a different plan from God's original, wherein he would take Jehovah's place here on earth. Lucifer promised that if he were given this opportunity "that one soul shall not be lost." While innocent and appealing on its face, the only way that Lucifer could make good on this promise would be to force everyone to either obey all the commandments or to force them to accept him as their redeemer. By forcing God's children to take one of those paths the agency of man would be compromised. The fact that Lucifer was attempting to "destroy the agency of man, which I, the Lord God had given him," and the fact that he wanted God's "honor" or "power" in return for his services, caused Lucifer to lose his place in the "authority and presence of God" (to be "cast down").
It should also be noted that Jehovah's response to Lucifer's plan was to assure God that Jehovah would do His will ("thy will be done"). Additionally Jehovah added "the glory be thine [God's] forever."
When God chose Jehovah, Lucifer "became angry" and "kept not his first estate." As he left the council in heaven "that day, many followed after him."  Following his angry exit from the council, Lucifer completed his fall and rebelled against "The Only Begotten Son," or Jehovah, thus starting the war in heaven. 
While Lucifer lead 1/3 of the heavenly hosts, Michael, or Adam as he was called on earth, lead those who fought against Lucifer. Not much is known of the mechanics of the war, except that in the end Lucifer was overcome by "by the blood of the Lamb, and by the word of their [Michael's followers] testimony." In this instance testimony most likely means "an official or legal declaration of what a person perceives as truth." This implies that Lucifer was overcome by declaring that the blood of the Lamb would be sufficient to enable those who came to earth to return to live with God. One could conclude that the "war" revolved around the faith in Jehovah to come to earth, live a perfect life, and do all of the other things necessary to become the redeemer while still retaining His and man's agency.
Expulsion of Lucifer and his Followers
Once Michael and his angels overcame Lucifer, Lucifer was "cast out" and "down to the earth" along with those who followed him. This suggests that the expulsion of Lucifer and his followers followed the creation of the earth, but was obviously prior to Michael's introduction to the Garden of Eden.
It is interesting to note that Lucifer does not gain the name of Satan until after his expulsion. This is evidenced by the revelation to the Prophet Joseph wherein he was told "...I caused that he should be cast down; and he became Satan, yea, even the devil, the father of all lies..."
Michael and his Followers
All who kept their “first estate” (premortal life) were promised that they would “be added upon”(which includes receiving mortal bodies). All who keep their second estate will have “glory added upon their heads for ever and ever” (Abraham 3:26).
The War in Our Day
The Bible dictionary in the LDS version of the bible adds:
- The warfare is continued in mortality in the conflict between right and wrong; between the gospel and false principles, etc. The same contestants and the same issues are doing battle, and the same salvation is at stake.
- Although one-third of the spirits became devils, the remaining two-thirds were not all equally valiant, there being every degree of devotion to Christ and the Father among them. The most diligent were chosen to be rulers in the kingdom (Abraham 3: 22-23). The nature of the conflict, however, is such that there could be no neutrals, then or now (Matthew 12: 30; 1 Nephi 14: 10; Alma 5: 38-40).
- [Abr. 4: 26]
- http://scriptures.lds.org/en/dc/76/25-26#25 Doctrine & Covenants 29: 36-37
- see [Doctrine and Covenants 29:36-38]
- see [Moses 4:1–4]; [D&C 76:25–28]; Isaiah 14:12–14
- It is interesting to note that while strikingly similar, there are two separate "castings" regarding Lucifer. One is his being "cast down" and the other is his being "cast out." While 'down' could refer to 'out', it is also possible that they were separate actions.
- [Abraham 3: 27-28]
- [Revelation 12:11]
- as defined by the entry under "[testimony]" in the "Guide to the Scriptures" on lds.org
- [Revelation 12:4, 7-9]
- [2 Peter 2:4]
- [Moses 4: 1-4] emphasis added