Revelation is "A Tale of Two Cities" which, Paul explains, represent two Covenants:
[Galatians 4:21-26 NASB20] (21) Tell me, you who want to be under law, do you not listen to the Law? (22) For it is written that Abraham had two sons, one by the slave woman and one by the free woman. (23) But the son by the slave woman was born according to the flesh, and the son by the free woman through the promise. (24) This is speaking allegorically, for these [women] are two covenants: one [coming] from Mount Sinai giving birth to children who are to be slaves; she is Hagar. (25) Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is enslaved with her children. (26) But the Jerusalem above is free; she is our mother.
In Revelation, one City/Covenant/Jerusalem is destroyed and the other descends from Heaven and represents the Bride/Body of Christ:
[Revelation 21:9-10 NASB20] (9) Then one of the seven angels who had the seven bowls, full of the seven last plagues, came and spoke with me, saying, "Come here, I will show you the bride, the wife of the Lamb." (10) And he carried me away in [the] Spirit to a great and high mountain, and showed me the holy city, Jerusalem, coming down out of heaven from God,
It is the violent destruction of Jerusalem via the Roman army c. 70 AD/CE and the arrival of the Bride/Body of Christ to prominence and power:
[Matthew 21:43 NKJV] (43) "Therefore I say to you, the kingdom of God will be taken from you and given to a nation bearing the fruits of it.