The Book of Revelation is thought to have been written during the reign of the Roman emperor Domitian (81-96 AD). Many Christians believe the author was the apostle John, but the consensus among scholars is that the book was written by an unknown author they call John of Patmos, who either lived on the Greek island of Patmos or was exiled there during one of Domitian's alleged persecutions of the early Christians.
Note: According to Christian sources, Domitian carried out several harsh persecutions, especially towards the end of his reign, but "some historians ... have maintained that there was little or no anti-Christian activity during Domitian's time." (Wikipedia) "The lack of consensus by historians about the extent of persecution during the reign of Domitian derives from the fact that while accounts of persecution exist, these accounts are very cursory or their reliability is debated." (That's a polite way of saying that a lot of the Christian stories about how they were persecuted in the ancient world are myths.)
It's commonly believed that the Book of Revelation describes Armageddon, the end of the world, but it seems more likely that its author was prophesying the fall of the hated Roman empire:
"Many people look to the Book of Revelations for signs of the apocalypse," according to a now-defunct source I found several years ago. "This event represents the cumulative battle between good and evil, ends the world, ushers in the Age of God. The Book of Revelations was written during a trying time in Christian and Jewish history. The book’s target was not necessarily Satan, but Rome. As a result, the final battle and victory of God over Satan was actually predicting the fall of the Roman Empire and the rise of Christianity."
According to biblical scholar L. Michael White, "most scholars now think that the issue revolved around the inauguration of the Flavian imperial cult in Ephesus ... Our clearest indication of how this is reflected in Revelation is seen in the description of the two 'beasts' from Rev. 13. The first is called 'the beast from the sea' who is given his power by Satan himself. He is described as having 'seven heads and ten horns,' and people worshiped him (Rev. 13.1-4). Then there is a second, 'the beast from the land' who makes everyone worship the first beast and its 'image' (Rev. 13.11-18). The 'image' (13.14-15) and the mysterious number '666' (13.18) refer to statues and coins or inscriptions with the emperor's image and titles. The 'beast from the land' probably referred to either the provincial governor of Asia or to the high priest of the imperial cult, who jointly would have overseen the temple and its festivals in Ephesus at just this time."
In other words, the apocalypse predicted by the Book of Revelation actually refers to the hoped-for collapse of Rome. If this view is correct, then all the millennial cults and end-times Christians who are waiting for Armageddon based on their reading of Revelation are actually waiting for an event which happened almost 1500 years ago. But the strange truth of all of this is that the Roman empire was already Christian when it collapsed in the west. Gibbon was at least partially right when he blamed the fall of Rome (partly) on "barbarians and Christianity."
Comment: It's strange and revealing that the New Testament, a collection of books about peace, love and redemption, should end with the apocalyptic bloodbath of Revelation. One minute, you have Jesus blessing the little children and talking about forgiving your enemies, then, the next minute, a beast with seven heads is slaughtering millions of sinners in a river of blood. That's quite a story arc, to say the least.
Revelation has always been my favorite book in the Bible because of its hallucinatory weirdness. Considering its surrealistic content, I've always wondered if John--assuming that was his real name--happened to stumble across some funny plants or mushrooms during his exile on Patmos, which, incidentally, was listed by Forbes (in 2014) as "Europe's most idyllic place to live." This has probably changed dramatically with the "refugee" invasion of the Greek islands, which has been an absolute disaster. The island probably wasn't that idyllic back in John's day, either, but the views must have been spectacular.