Milllennialism refers to the belief in a literal, earthly thousand year reign of Jesus, based on a statement from the Apocalypse of St. John (aka the Book of Revelation). It is in contrast to Amillennialism which interprets the thousand years as non-literal and a reference to Jesus' reign in heaven since His ascension.
In most modern contexts one usually hears Millennialism in the context of Premillennialism, which is in reference to the timing of Christ's return or Parousia, namely Premillennialism says that Christ returns before (pre) the Millennium. Premillennialism is in contrast to Postmillennialism, that Christ returns after (post) the Millennium. Postmillennialism has very few adherents today and has generally only been associated with some forms of Neo-Calvinism, such as the New Divinity of the 1800's, and in the 20th century has largely been restricted to the adherents of the ideas of R. J. Rushdoony who is the father of Christian Reconstructionism, aka Dominionism. Postmillennialists generally believe that the Millennium is a period of peace and prosperity on the earth that will be accomplished through the work of the Church influencing and transforming society into a godly utopia through the institution of Theonomy in secular institutions, that is, by making society and nations "Christian" the Church will lead the earth into the Millennium, and afterward Christ will return.
Again, Amillennialism is at odds with both Pre and Postmillennialism; maintaining that "The Millennium" is figurative and symbolic language referring to Christ's reign since His ascension. Amillennialism has historically been the majority opinion of most Christians throughout history and is representative of Catholic, Orthodox, and Historic Mainline Protestant belief. However Millennialism was a popular view among some of the early Christian fathers such as Justin, Irenaeus, and Hippolytus.
-CryptoLutheran
