The Revelation of John of Patmos was written to Christians of the first century in a very difficult time with persecution past, present and ahead. John needed to code his writing a little because, for instance, if he had used Nero’s name instead of the Beast he would have been executed right away very likely instead of exiled to a prison island.
Martin Luther said that the Revelation of John has ‘a lot of straw’ in it. That reference is to brick making I believe, wherein one may add filler to the brick that isn’t purely necessary.
My opinion is that the apocalypse occurred in the first century with Jesus crucified, the Christians scattered, Apostles such as James and Paul killed, Jerusalem destroyed. This is the era where the Kingdom of God is building up. That will continue until Jesus returns physically.
The events of the Revelation are not all complete for the Universe still continues obviously. Some people want to sell all sorts of pre-tribulation ideas in churches because it makes for good disaster scenarios and social irresponsibility for the condition of the world. It is something of a cult point of view that I don’t share. The subject isn’t simple.
Jesus will return to judge the quick and the dead. I have written something about eschatology in a book I made of a theology course I took. It is free to download. Page 38 and after has some material explaining something of my opinion.