Revelation 1:9

9 I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.

John tells us where he was located and says those he is writing to are brothers in the kingdom. That includes all believers. John was exiled to an island called Patmos. Some think they tried to kill John and could not, so they exiled him to this island. (There are a few hints of this in ancient writings).

Certainly, God would not have allowed John to die before this book was written. John says he was imprisoned there for teaching the scriptures and giving the testimony about Jesus Christ. He was not the only one in tribulation during that period. All the apostles had been killed at this point and the Jews were actively persecuting the Church. In this verse, John talks about the kingdom and patience of Jesus Christ. Jesus has been very patient for about two-thousand years now so that the bride given to Him by the Father would be complete.