What will happen at the end of the thousand-year reign?
The millennial reign will end, and there will be a complete change in the Creation and the Universe. Believers then enter Eternity, which will be on much the same basis as the Kingdom: nations will exist again, and Christ will rule and reign from the New Jerusalem.
Les explains that the thousand-year reign of Christ is really just an introduction into the Eternal. Even though the millennial reign will end, and there will be a complete change in the Creation and the Universe, when we enter into Eternity it will be on pretty much the same basis as the Kingdom. There will be nations again, and Christ will be ruling and reigning from the New Jerusalem. The thousand-year reign will also have to be another time of testing, because those who come into the Kingdom are only believers—Gentiles who believed during the Tribulation under the 144,000's preaching, and the remnant of Israel will be saved.