No human on earth knows all the details, but we do know that Satan decided he wanted to be like God in his heart. He sold the same lie to a third of the angels in heaven. He entered the Garden to purposely try to usurp the Lord there too with Adam and Eve.
Everyone who sins, no matter what particular sin, commits sin against God. Everyone who sins, buys into the lie from the father of lies, the father of mutiny in that: You can be like God. You can do what you want, when you want, how you want. You do not have to listen to God. Be your own god. That is “the lie.”
The truth is: God is #1. He made everything including the rules. Rule # 1 is God is God. Not you or I and certainly not the devil. Disobedience is expensive; no one can afford it, as it separates us from what we were made for and that is wonderful fellowship with our Father God.
So how does “the war” work since the devil was cast out of heaven to earth and did his dirty-work in the Garden?
There is a constant battle for our souls. God wants us to make heaven and tries to help us while the devil seeks to kill and destroy humans. Every person that falls for the lie that God does not have to be honored and obeyed is a soul for the devil.
Where Christians are, there is Light. Where the lost are, there is darkness. Demonic forces use humans. Demonic forces are empowered by using humans. The devil wants to rid the earth of Christians and as more people choose against God, the earth will grow darker and the devil will be more empowered. We as humans cannot normally see in the spirit, but we sure see the results. The situation is real. Once before, the whole earth grew spiritually dark and had to be cleansed with a Flood and God did a “re-start” with Noah and his family. Today, we are near the End of this Age. This is it. We are approaching final curtain call.
If we choose God and obedience to Him, we are empowered in the Light. If we choose the lie, rooted from the master liar and mutineer, then we belong to darkness.
Righteous decisions and actions empower heaven to work. Disobedience to God empowers evil to work. One might say, I choose neither. To not choose, is still disobedience to God.
The more darkness the devil can develop in people of disobedience, the more power he has. God is all-powerful. But He gave us the option of free will (though the consequences of sin is death, He offers a pardon to those who repent and accept and follow Jesus Christ). So until the “time of choice” is over, God allows a certain amount of choice, even against Him. But there will come a day of reckoning.
The goal of Satan is the end of Christianity on earth and to take heaven by force. He is still full of his rebellious and mutinous self. And the end is still clear. God wins. Even if Christians get caught in the devil's cross hairs, the worst he can do is take our bodies. When handling the thoughts of extreme persecution and possibly death, we need to combat fear by remembering the words of our Lord, “And do not fear those who kill the body but cannot kill the soul. But rather fear Him who is able to destroy both soul and body in hell.”
And take total heart in: "I am the resurrection and the life. He who believes in Me, though he may die, he shall live. And whoever lives and believes in Me shall never die. Do you believe this?"
Take heart, hold fast and press in close to the Lord, for the final countdown is approaching fast, ready or not.