myelaine...This "great crowd" in Revelation 19:6-8 is already in "heaven," see v. 1.
holly....Here's my take on it. The kingdom is "God's rule" which has both ethical and apocalyptic dimensions. Check out what the whole "good news of the kingdom" is in Matthew. It's not about a coming government that will crush worldly governments, but mostly about how to treat others and "do the will of God". This is the whole focus of Jesus' teaching, his parables, the Sermon on the Mount. Note also how "Let your kingdom come" in the Lord's Prayer (cf. Luke 11:2) is interpreted in Matthew 6:10 as establishing God's "will" on earth. One's destiny in the "kingdom of heaven" (note that Matthew almost always refers to it as the "kingdom of heaven") depends entirely on how one lives one's life (cf. Matthew 5:20, 6:33), and God's rule is manifest in those who do his will. "Not everyone who says to me, ?Lord, Lord,? will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven" (Matthew 7:21). The kingdom was already present through the Holy Spirit (Matthew 12:28), and since early Christians believed that they were given the Holy Spirit, so was the kingdom already present through their works. The community of Christians living according God's will were given authority to forgive sins -- something previously restricted to God -- and they were allowed to do on earth what is done in heaven (Matthew 16:19, 18:18; compare with 23:13, wherein the Pharisees who do not do God's will "shut the kingdom of heaven in men's faces"). Through the apostles and through the Holy Spirit, the kingdom was already present, but it was "hidden" and "tiny" to the rest of the world, so that most do not recognize it (Matthew 13:31, 33, 44). There is still an apocalyptic element here too. The kingdom represented on earth by the Christian community precedes the judgment of the whole earth by the Son of Man who would confine the unrighteous into Gehenna while everyone else doing God's will would receive the blessing of the kingdom. Thus, the Christians are presently the "sons of the kingdom" (Matthew 13:38) who precede the "harvest at the end of the age" and during the harvest, the Son of Man "will send out his angels, and they will weed out of his kingdom everything that causes sin and all who do evil" (v. 41). This leaves only the righteous who will inherit the kingdom of heaven.
This is the ethically-focused Jewish-Christian perspective in Matthew, which stresses salvation by works (cf. also James). Paul had a very different point of view and replaced this ethical concept of justification with justification by faith. Since modern Christian churches are influenced more by the salvation-by-faith of Paul and John than the view in Matthew, this may explain why you did not hear so much about the "kingdom". Paul clearly describes the kingdom as heavenly (1 Corinthians 15:50; cf. 2 Timothy 4:18), so it is understandable if the "kingdom of God" is understood to refer to heaven; Paul frequently referred to the Christian destiny as heaven, (cf. 2 Corinthians 5:1, Philippians 3:20, Colossians 1:5, 1 Thessalonians 4:16-17), and regarded Paradise as presently in heaven in accordance with common Jewish thought of the day (2 Corinthians 12:2). Intertestamental texts (such as in 2 Baruch and 4 Ezra) describe that in the future the heavenly Paradise would descend from heaven to the earth, with the sword removed from the Tree of Life and with everyone righteous being able to eat again from the Tree of Life, and Revelation clearly relates a similar concept of heavenly New Jerusalem descending to a "new earth" (not to be confused with the present earth, which would be destroyed, cf. also 2 Peter 3), where the righteous would dwell in God's presence, and outside the city walls would dwell the wicked and those punished forever. The concept is a little similar to Matthew 8:11-12 which has the righteous feasting with Abraham, Isaac, and Jacob inside the kingdom of heaven, "but the subjects of the kingdom will be thrown outside, into the darkness, where there will be weeping and gnashing of teeth". Of course, not all Christians had such a concept as found in Matthew or Revelation, and well-developed chiliasm was a minority view in the early church; it prevailed mostly in Asia Minor.