I’m not religious, but some people are still waiting for it to happen. Do some people believe it already happened?
I’m not religious either but I was raised to be very religious. I definitely read the Bible, and I did my best to understand Revelation. I was discouraged from reading it because supposedly it was too difficult and confusing to understand but that didn’t stop me. One of the weirdest things I remember from Revelation was a dragon trying to catch a baby that a woman was about to give birth to. The dragon was going to swallow it.
Another is of the Seven Arch-Angels with trumpets, especially the seventh with one foot on land and the other on sea, swearing that “Time shall be no more!” Before that, if I remember correctly, came all kinds of plagues similar to the Plagues of Egypt that Moses used to force Pharaoh to let the ancient Israelite slaves go. Each of the Arch-Angels blasted his trumpet, letting loose his own particular war or pestilence or plague. The seventh ended Time, and I guess that was it. Except the book did not end there.
There is also a part about a great lament reverberating throughout the cosmos that, “Babylon has fallen!” The writer of Revelation, as well as Christians ever since, attach cosmic meaning to the images in the book. Each new generation interprets Revelation in its own way to fit its own time. To answer your question “Has Revelation already happened,” you can read it online, starting with Revelation 1 and continuing to the end, then form your own opinion.