Peter wrote to the believers in the Roman-occupied middle east, in the country we now know as Turkey. There must have been some significant persecution, because the second half of the letter is encouraging them to stand through their suffering:
1 Peter 4:1 So then, since Christ suffered physical pain, you must arm yourselves with the same attitude he had, and be ready to suffer, too. For if you have suffered physically for Christ, you have finished with sin.
They were not to be resentful to God or anyone else because of what they were going through:
1 Peter 4:13 Instead, be very glad—for these trials make you partners with Christ in his suffering, so that you will have the wonderful joy of seeing his glory when it is revealed to all the world.
So where were these believers?