He is limited because the Gospel prevents him from keeping the world in bondage to sin, and because the Gospel has leavened the world so that even unbelievers can no longer believe the foolishness they believed in the past. How many of your friends offer blood sacrifices to a variety of demons today? When Paul walked around the Roman empire, that's what they did everywhere, in every city. Even among unbelievers, Christianity had an effect on the way people thought about God and the way they lived, their ideas of what was good and what was permissible. No doubt the devil would prefer to have everyone prostrating themselves in front of statues of Moloch and burning their children in his honor, but once the Gospel came to the west, people wouldn't accept that anymore. He had to create false religions that looked holier than true Christianity.
But the main thing is that he no longer can keep people in bondage to sin and damnation where the Gospel is preached. Prior to the Gospel going into all the world, the devil held most of the world in slavery from which they could not get out, and their sacrifices and religious efforts only made it worse.
He can't do that anymore, because when the Gospel is preached, it makes people free. Not that they don't suffer physically anymore, but that they are free spiritually. No longer condemned. No longer bearing their sins. That is the greatest chain imaginable on the devil.
As far as a detailed discussion of Revelation 19, I'm afraid I'm not up for it tonight. I will read it again and maybe discuss it with you some other time. What would probably be more helpful is for you to research how Calvin, Luther, Augustine, and others read Revelation 19, and do some further research on the origins of Christian millenarianism. The fact that no Christians believed that the millenium was literal until a century and a half ago doesn't mean that they are right. But neither Luther nor Calvin (nor Augustine) were men who thought Scripture was something to play around with to get whatever answer you wanted. They revered it as the word of God. Luther staked his life on it and was willing to go against the whole hierarchy of the church and its theologians rather than depart from God's Word, and believed that Scripture should be taken in its literal sense except when it was clearly speaking figuratively. So the question is, why is there no one prior to the 19th century who agrees with the pre-millennial end times theory that American evangelicals think is indisputable?