What Was the Historical Confluence of Events Around This Book?

Revelation was written on one of the Mediterranean islands known as Patmos which is off the coast of Ephesus. John says in Revelation that he's on Patmos because of the testimony of Jesus Christ and that could just mean he was there evangelizing people but according to various early Christian sources they say that the emperor had banished him there. The next question is well which emperor banished him and that deals with what decade the book was written now it everybody pretty much agrees it's written in the first century but the question is when.