Premillennialism believes in Christ's physical return before a literal 1,000-year earthly reign, with historic premillennialism placing it after the tribulation and dispensational premillennialism holding a pre-tribulation rapture of the church.
Postmillennialism is a Christian belief that Christ will return after a period of Christian prosperity in which the church's influence will transform society through the gospel.
Christians and churches will face hardships from Satan, but by remaining faithful to Jesus, they can trust in God's power to limit evil and reward their perseverance.