And
Verses 19, 20, and 21 contain the consequences of the GREAT EARTHQUAKE (previous verse).
In scripture, only Jerusalem (where Jesus was crucified, Revelation 11:8) is referred to as the GREAT CITY. Having said this, it should be noted that scholars have identified the GREAT CITY variously as Rome, Jerusalem, or Babylon. Since all three cities are close to tectonic boundaries, it is plausible that physically any one of them could split into three parts.
Symbolically, this could be a spiritual split of Jerusalem into three factions. For example, Arabs, Jews, and Gentiles or, perhaps, Palestinians, Orthodox Jews, and Moderate Jews. This may be the visionary way of showing that the Unholy Trinity is having a difference of opinion among its ruling ranks.
The whole world is affected by this GREAT EARTHQUAKE. Previously in the 6th seal's GREAT EARTHQUAKE (Revelation 6:12), cities may have escaped the massive destruction and death that usually accompanies these events. In this last GREAT EARTHQUAKE, already weakened cities worldwide fall.
Carrying the symbolic viewpoint forward, the Antichrist loses control of the cities of the world. Perhaps the people who took the mark of the beast suddenly, like an earthquake, realize that they have been deceived by the great deceiver (Revelation 12:9).
This may be the fulfillment of Isaiah's prophecy (Isaiah 13:1-16).
Just as God promised to remember his covenant with Israel (Psalm 98:3, Psalm 105:8-15, Psalm 105:37-42), so, too, He will remember BABLYON THE GREAT with the cup of the wine of HIS FIERCE WRATH (Psalm 137).
As we will find in following topics, Babylon can be considered as the sum of the evil social, religious, and political worlds. God now focuses His full attention on this Devil-assisted but manmade structure.