Fallen Fallen is Babylon the Great, which gives us a timeline we can attach to. Rev. 18 has Fallen Fallen to line up with. Any changes that take place for the 144,000 are from the same time as Rev. 18.
This is a sign of what the 144,000 will preach. Until now, they have been preaching Fear God, but this will change when the next angel cries out.
Now we have another event to align the 144000 with. You will see in Chapter 17 that this is likely a collapse of the USA. In Rev. 18, you have three events. Fallen Fallen, gone in a day, or financial collapse, and cites burnt down in an hour. This change could be a takeover of power from one set of rulers behind the scenes to another.
Since Bill Clinton, the leadership of the USA has been descending into nothing better than post-modern gangsters. At some point, a line crossed where the old rulers lost control. These old rulers are from Europe, and hence Revelations says the ten will look upon the harlot with hatred. This happens just before or near the beginning of the 1260 reign of the Antichrist, although the two events do not seem to be related. The clue is in what is preached next, do not take the mark of the beast. The call to preach Fear God is something that happens before or at the beginning of the Forth Beasts' reign. We will look closely at Fallen Fallen when we get to Rev. 17 and 18.