Legions of Angels
Satan's attempt to conquer heaven failed. The forces of the Devil were defeated by an army of righteous angels under the command of the archangel Michael. At the end of the battle, Satan and his crushed army of "fallen angels" (hence the term) were scattered over the earth i.e. "he was cast out into the earth, and his angels were cast out with him."
"14:13 For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:
14:14 I will ascend above the heights of the clouds; I will be like the most High." (Isaiah 14:13 KJV)
"12:7 And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, 12:8 And prevailed not; neither was their place found any more in heaven. 12:9 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 12:7-9 KJV)
"Michael and his angels fought against the dragon and his angels"
The English word "legion" originated from a Latin word which meant to collect. The Roman empire used it as a military designation for a large formation of troops, ranging from 3,000 to 6,000 infantry, plus cavalry. In the time of the New Testament record, with the land of Israel under Roman military occupation, it was a familiar term used by the military and civilians alike. Even angels used it, as in this example of a large section of Satan's defeated and scattered army ("they were about two thousand") referring to themselves as "legion."
"5:9 And he asked him, What is thy name?
And he answered, saying, My name is Legion: for we are many.
5:10 And he besought him much that he would not send them away out of the country.
5:11 Now there was there nigh unto the mountains a great herd of swine feeding.
5:12 And all the devils besought him, saying, Send us into the swine, that we may enter into them.
5:13 And forthwith Jesus gave them leave. And the unclean spirits went out, and entered into the swine: and the herd ran violently down a steep place into the sea, they were about two thousand; and were choked in the sea.
5:14 And they that fed the swine fled, and told it in the city, and in the country. And they went out to see what it was that was done. 5:15 And they come to Jesus, and see him that was possessed with the devil, and had the legion, sitting, and clothed, and in his right mind: and they were afraid. 5:16 And they that saw it told them how it befell to him that was possessed with the devil, and also concerning the swine." (Mark 5:9-15 KJV)
Jesus Christ also used the term to refer to the force of righteous angels that were at His command. The Sacrifice of The Lamb of God was allowed to happen; it was not a victory for Satan.
"26:53 Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels? 26:54 But how then shall the scriptures be fulfilled, that thus it must be?" (Matthew 26:53-54)
Upon His return, the legions of angels that defeated Satan (as described in the verses above) in the heavens will come to earth with the Messiah and complete the victory here.
"19:11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.
19:12 His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself. 19:13 And he was clothed with a vesture dipped in blood: and his name is called The Word of God. 19:14 And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean. 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God. 19:16 And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS.
19:17 And I saw an angel standing in the sun; and he cried with a loud voice, saying to all the fowls that fly in the midst of heaven, Come and gather yourselves together unto the supper of the great God; 19:18 That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them, and the flesh of all men, both free and bond, both small and great.
19:19 And I saw the beast, and the kings of the earth, and their armies, gathered together to make war against him that sat on the horse, and against his army. 19:20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone. 19:21 And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh." (Revelation 19:11-21 KJV)
20:1 And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand. 20:2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years, 20:3 And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season. 20:4 And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years." (Revelation 20:1-4 KJV)
Fact Finder: What is the Messiah going to use His legions of angels to accomplish on earth?
See Christ the Conqueror For Peace