Originally posted by Astner
The war specified in Revelations will take place at the end-times.
A war did happen in Heaven, and still continues this day. Satan was cast from Heaven, and fell to Earth.
Revelation 12:7-12 talks about the casting out of Satan-two times. One was at the beginning when he rebelled in Heaven, just before creation of life on earth, and the second was at Calvary.
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 12:7-9)
This war was in Heaven; two groups against each other-
Michael and the loyal angels on one side, and Satan and his angels on the other side. In this first battle Satan and his sympathizers lost their place in Heaven. They were thrown out from Heaven to earth.
Obviously, this earth was still uninhabited. It was "without form and void and darkness was on the face of the deep" (Genesis 1:2).
God had to throw him out of Heaven into a particular place. As the whole universe is God's, Satan had to be somewhere in God's vast creation. And earth was the place.
And when God created life on planet earth (according to His prior plan and set time), He warned Adam and Eve of this wily foe.
Satan would not have got a hold on this planet had Adam and Eve stood the simplest of test, just once! God then would have cut short the time period of Satan.