Matthew 24:21

Matthew 24:21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.

John identified himself as a brother in tribulation showing this is not something that just pounced on man but has been all the while.
The tribulation which started with Cain has been increasing steadily and now gets to a climax that it had never gotten nor will ever get.