The kingdom of darkness has exercised authority over the world for the past several millennia, but that is all about to come to an end. It has been prophesied that Jesus will return, and when He does, He will bring an end to Satan's dominion.
At some point, Satan and his angels will be banished from heaven and thrown down to the earth. When this happens, he knows that his time is short, so he joins with the beast and the false prophet to form an evil trio which will wage war against God's people. Their attack against Israel fails so they focus their persecution on those who hold to the testimony of Jesus.
The mark and the image will be the means by which the evil trio will identify and persecute those who believe in Jesus the Messiah. It will bring about the great tribulation, a time when those who worship God are called on to persevere in their faith in Jesus.