the great city - the capital and seat of the apostate Church, spiritual Babylon (of which Rome is the representative, if one literal city be meant). The city in Rev 11:8 (see on Rev 11:8), is probably distinct, namely, Jerusalem under Antichrist (the beast, who is distinct from the harlot or apostate Church). In Rev 11:13 only a tenth of Jerusalem falls whereas here the city (Babylon) “became (Greek) into three parts” by the earthquake.
cities of the nations - other great cities in league with spiritual Babylon.
great ... came in remembrance - Greek, “Babylon the great was remembered” (Rev 18:5). It is now that the last call to escape from Babylon is given to God’s people in her (Rev 18:4).
fierceness - the boiling over outburst of His wrath (Greek, “thumou orgees”), compare Note, see on Rev 14:10.