As some may be seeking a clarification of postmillennialism, it is fitting to express what postmillennial theologians actually do believe. There is always the risk of oversimplification when criticizing someone else's viewpoints.
Greg Bahnsen's book "Victory in Jesus: The Bright Hope of Postmillennialism" is an accumulation of five separate lectures given on the subject of postmillennialism. In the lecture title "The Triumph of the Gospel", he includes a small section outlining the basic tennets of postmillennialism. Now these are not unique to postmillennialism (meaning other views certainly can share them) but must be affirmed by all Bible believing postmillennialist.
I won't quote the section completely since I'd prefer you go and buy the book for yourself! Heck, ask nice and I might buy a copy for you! Without further ado....
1. As postmillennialists we champion the inspiration, infallibility and sole doctrinal authority of the Bible...
2. We are not postmillennialists because we have some kind of understanding of man's inherent goodness. Evangelical postmillennialists believe that fallen man it totally unable to do any saving good, cannot atone for his sins, and cannot become a member of the kingdom of God except through the redemptive work of the Savior and the regeneration work of the Holy Spirit...
3. Postmillennialists teach the glorious personal return of Jesus Christ at the end of history to judge the world...
4. We insist that at His first advent, Jesus, the Son of God, came as the messianic mediatorial King and established His saving kingdom among men on earth...We believe that Jesus is presently the King...
5. Postmillennialist are painfully aware that those who belong to the Lord Jesus Christ-the church itself-those who belong to Him-are appointed to suffering in this world...You will be afflicted in this world. So we are not whistling in the dark or engaging in some kind of Pollyanna wishing thinking. This is not postmillennialism.
6. Postmillennialist believe that the gospel is to be preached to all nations, by the Church, prior to the second advent of Christ. Eventually, this will bring worldwide conversion...
7. Postmillennialism maintains that the victorious advance of Christ's kingdom in this world will take place in terms of the present peaceful and spiritual power of the gospel, rather than through a radically different principle of operation, namely, physical force and earthly violence in order to subdue opposition...
8. Postmillennialism believes in the gradual growth and success of the kingdom of god by the power of the Holy Spirit working through the Church's preaching of the gospel...
9. Postmillennialists are not committed to the view that each and every individual on earth is going to be saved...
10. Postmillennialists believe that there will be a final apostasy-a falling away just prior to the return of Christ, and that Satan will be loosed and he will deceive the nations again...