The final section of the Revelation, chapters 17 – 22, give us a much more detailed description of the end of the world as we know it than we have seen thus far.
But first remember something: this book was written in troublesome times to first century people. The book has maintained that the kingdoms of the world, particularly the empire of Rome, is being influenced by Satan but everything is under the control of God. At the end of chapter 19, the power and influence of Satan is drastically reduced as Satan is thrown into the abyss. A long period of time follows, described in Revelation as a thousand years (chapter 20).
During this long period of time – not “just” a thousand years since few of the numbers in this book are literal – those who have been martyred for their faith enjoy an exalted status with Christ, a status promised to all Christians but realized early by the martyrs. At the end of that time, Satan will be released to inflict unbridled pain on God’s people. But he will not succeed. Before a final planned conflict begins, he will be removed by God forever.
If he is going to be removed forever, why not remove him now?
I do not know. The point is, everything is subject to the eternal plan and power of God.
Are we in the long period (thousand years), or is it to come?
It would seem to me that since the long period began with the end of the Roman empire, we are now in that long period. Satan may be restrained (bound with a chain), but we can expect his influence only to continue and become stronger. We can also expect that God will, in His time, bring it all to an end.