Central thesis: Jesus Christ will after the millennium.
The millennium is not to be understood as a literal thousand years.
Various views of the time to which "millennium" applies:
The period between Christ's first and second advents.
The "golden age of peace and righteousness" that will be brought in after the preaching of the gospel has gone on for a period of time.
The present age will develop morally and spiritually until the golden age arrives.
Boettner, "Postmillennialism is that view of the last things which holds that the kingdom of God is now being extended in the world through the preaching of the gospel and the saving work of the Holy Spirit in the hearts of individuals, that the world eventually is to be Christianized and that the return of Christ is to occur at the close of a long period of righteousness and peace commonly called the millennium. It should be added that on postmillennial principles the Second Coming of Christ will be followed immediately by the general resurrection, the general judgment, and the introduction of heaven and hell in their fullness." (Ref. Loraine Boettner, "Postmillennialism," in The Meaning of the Millennium: Four Views, ed. R. Clouse (Downers Grove, Ill.: InterVarsity, 1977), pg 117)
Two types of postmillennialism:
Biblical Postmillennialism: the world's improvement will come by the preaching of the gospel as the Holy Spirit transforms more and more people.
Focus: personal transformation
Mechanism: Biblical evangelization.
Liberal Postmillennialism: the world's improvement will come by mankind's innate capability and tendency for improvement toward ultimate goodness.
Focus: societal transformation
Mechanism: societal activism
Basic tenets:
Christ will return after the millennium
The millennium's length is undetermined
The Kingdom is spiritual, Christ's rule in believers' hearts; and is not a literal, earthly reign of Christ.