A War in Heaven
"And there was war in Heaven: Michael and his angels fought against the dragon [Satan],... And... [Satan], 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: 7-9)
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Book of Mormon people were taught and knew about events that took place previous to us coming to this Earth, as recorded in the Bible and as revealed to latter-day Prophets.
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<<Hubert Howe Bancroft an American Historian
"...Mexican, [native Mesoamerica inhabitants], Mythology records of the war in Heaven, and the fall of Zontemonque [Satan] and other rebellious spirits..." (The Native Races, The works of Hubert Howe Bancroft, 1886,Vol. V, Internet Archive, Origin of the Americans p. 12). ("war in Heaven" p. 90)
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Additional Information
War in Heaven (Bible Dictionary, Church of Jesus Christ of Latter-Day Saints)
The War in Heaven (President Gordon B. Hinckley) 2:05 min.
The Dawning of a Brighter Day (President Gordon B. Hinckley, Ensign, May 2004)