The invisible war started in heaven with Lucifer, originally a beautiful angel created by God and exalted to a high place of prominence.
And war broke out in heaven: Michael and his angels fought against the dragon; and the dragon and his angels fought. But they did not prevail, nor was a place found for them in heaven any longer. (Revelation 12:7-8)
The name Lucifer means "brightness" or that which "shines." The reason the enemy is no longer called by this name in Scripture is because his character has changed. He is now called Satan which means "adversary, accuser, or slanderer."
Lucifer arrogantly decided to try to take over God's Kingdom. The account of his rebellion is recorded in Isaiah 14:12-17 and in Ezekiel 28:12-19.
A group of angels joined Lucifer in this revolution. Lucifer and these sinful angels were cast out of heaven by God's holy angels and formed their own evil kingdom:
So the great dragon was cast out, that serpent of old, called the Devil and Satan, who deceives the whole world; he was cast to the earth, and his angels were cast out with him. (Revelation 12:9)
Jesus witnessed this event taking place.
And He said to them, "I saw Satan fall like lightning from heaven." (Luke 10:18)
Notice that Jesus did not say that He was involved in the battle. Remember that the battle is not between God and Satan, but rather between submission and rebellion. Those who have submitted themselves to God (holy angels and redeemed men) battle against those who have rebelled (fallen angels and unredeemed men).
Also note that it is Satan and his angels who fell, whereas man died. The Bible does not say that mankind is fallen. It says we are dead in our sins. The word "death" in Scripture means separation, meaning our sins have separated us from God:
And you He made alive, who were dead in trespasses and sins, in which you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience. (Ephesians 2:1-2)
You were dead in sin, but now you are alive to God. You no longer walk in the ways of this evil world or according to the dictates of your flesh. You know how the battle started, who was responsible for it, and what to do about it. This knowledge is preparing you to wage effective spiritual warfare.
My FATHER, My God, this year let my life reflect the blessing of the Lord, I shall not be static, I decree PROGRESS, FAVOR, HONOR, AND INFLUENCE are my portion. My life is SALTED, My speech is SALTED, My Home and Business are SALTED in the name of Jesus.