Revelation 20:9

9  And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.

The Kingdom of Jesus will last forever according to scripture but Satan obviously has deceived these into thinking that since the millennial reign is complete, that God is done with rule from Jerusalem by the saints. It is a wrong assumption.

Some scholars think that most in the body of Christ during this thousand-year period will not live on earth but will actually live in the Holy City that is in heaven. Like the angels of Jacob’s ladder, they may be ascending and descending from the Holy City to carry out their assignments (Genesis 28:12). I think that is correct because all saved people could not fit in the the area of Israel allotted.

After death is conquered and the thousand years, it is my conjecture that Christ will offer up the kingdom to the Father (1 Corinthians 15:24) and withdraw to the Holy City where His bride is. By doing so, Jesus will leave the affairs of the kingdom on earth to the natural saints that rule on earth in Israel. Satan will see this as an opportunity to again deceive the world like he did Adam and Eve. Satan could not ascend out of the pit and deceive the world as long as Jesus was ruling on the earth anyway. God will give Satan enough rope to hang himself and this he will do. 

The removal of the administration over the earth by those in the spiritual body of Christ will allow Satan to ascend out of the pit and to deceive the world with the same lie he insinuated in the Garden of Eden that man would become like God. Now he will say that they have achieved it. The earth during the thousand years becomes like the Garden of Eden and natural death will even be conquered.

The release of this lying spirit on the earth will convince many that since death has been conquered, they  no longer need to submit to God's saints ruling from Jerusalem and they will come against them. Many in the world will rebel against this government in Israel and seek to live as gods of their own soul. When the world is deceived to come against the camps of Israel to overthrow the saint’s rule on earth, fire will come down from heaven from God and devour them all.