What exactly is "The Millenium"?
Nobody is in agreement on that one . All we can do for you is explain our own position on the matter and you will need to read everything for yourself and make your own decision. People get very adamant about what they think is going to happen.
This is my view---there are others:
2Th_2:8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
2Pe_3:10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.
2Pe_3:12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat?
1Th 4:15 For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.
1Th 4:16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:
1Th 4:17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Jer 4:23 I beheld the earth, and, lo, it was without form, and void; and the heavens, and they had no light.
Jer 4:24 I beheld the mountains, and, lo, they trembled, and all the hills moved lightly.
Jer 4:25 I beheld, and, lo, there was no man, and all the birds of the heavens were fled.
Jer 4:26 I beheld, and, lo, the fruitful place was a wilderness, and all the cities thereof were broken down at the presence of the LORD, and by his fierce anger.
Jer 4:27 For thus hath the LORD said, The whole land shall be desolate; yet will I not make a full end.
Jer 4:28 For this shall the earth mourn, and the heavens above be black: because I have spoken it, I have purposed it, and will not repent, neither will I turn back from it.
Zep 1:14 The great day of the LORD is near, it is near, and hasteth greatly, even the voice of the day of the LORD: the mighty man shall cry there bitterly.
Zep 1:15 That day is a day of wrath, a day of trouble and distress, a day of wasteness and desolation, a day of darkness and gloominess, a day of clouds and thick darkness,
Zep 1:16 A day of the trumpet and alarm against the fenced cities, and against the high towers.
Zep 1:17 And I will bring distress upon men, that they shall walk like blind men, because they have sinned against the LORD: and their blood shall be poured out as dust, and their flesh as the dung.
Zep 1:18 Neither their silver nor their gold shall be able to deliver them in the day of the LORD'S wrath; but the whole land shall be devoured by the fire of his jealousy: for he shall make even a speedy riddance of all them that dwell in the land.
Rev 20:5 But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection.
Rev 20:6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
When Jesus returns the saved dead are resurrected, those that are alive are changed and all go to Jesus in the clouds to be with Him. The wicked are destroyed, the heavens and the earth are destroyed and left empty and void---What is there left to reign over??
We go to the New Jerusalem with Jesus to the Holy City for the 1000 years. After the 1000 years is the judgment of the wicked. Death and hell are cast into the lake of fire. After that, we and the city come down after the earth and heaven are remade.
Rev 21:1 And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.
Rev 21:2 And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband.
It is symbolized with the 7th year of rest for the land:
Lev 25:3 Six years thou shalt sow thy field, and six years thou shalt prune thy vineyard, and gather in the fruit thereof;
Lev 25:4 But in the seventh year shall be a sabbath of rest unto the land, a sabbath for the LORD: thou shalt neither sow thy field, nor prune thy vineyard.
Lev 25:5 That which groweth of its own accord of thy harvest thou shalt not reap, neither gather the grapes of thy vine undressed: for it is a year of rest unto the land.
The 7th day Sabbath also points to that rest.