Postmillennialism is a belief about when Jesus Christ will come back to the world. It is based on a belief that Jesus will return to the world after most people have become Christian and the world is at peace. This belief is different than premillennialism, which believes that Jesus will come back to the world before most people become Christian and the world has become peaceful. Postmillennialism believes that Jesus will come back after most people have chosen to follow him and the world is at peace.