Rev 16 - has Armageddon - in that section "something" goes to the governments of "all the Earth" and tells them to assemble their armies and weapons at a given location for war. In Rev 19 we see the armies all assembled and ready for war. Who are they fighting in Rev 19?
Answer: "The second Coming of Christ" coming down out of heaven with "armies" according to Rev 19.
How in the world did governments of the Earth ever get convinced that something would be coming down out of the sky - from "space".
One thing is for sure - they were not told "Jesus the Savior of the World is coming to gather His saints". They were told "Some other story"
You bring up a very important point. That they have to know ahead of time, to amass their armies for war. I was discussing with my mother not too long ago, because this had occurred to me as well. I think the answer is staring us in the face.
Consider these points:
1. Every eye will see Him and all kindreds of the earth will wail because of Him (Revelation 1:7).
2. Men of all kinds, from kings of the earth to the common man, will hide themselves in the dens and in the rocks of the mountains (Revelation 6:15-17). They are hiding from His face.
3. Heaven opens up and Jesus comes with His armies, to make war (Revelation 19:11-14).
4. The birds are called to the supper of the great God, just before Jesus arrives (Revelation 19:15-18).
5. The beast and the kings of the earth gather together to make war with Jesus (Revelation 19:19).
What do all of these points have in common? They require
time to take place (especially 2 and 5), which points to the visibility of Jesus as a prolonged event that all will see.
At first, only the beast and the kings of the earth will be aware, because they will see Him coming from afar. i.e. Who has the most advanced technologies in the world? Who owns a telescope named after a fallen being? There's no need for them to be told or there to be a Project Blue Beam type scenario.
At some point, the heaven rolls back like a scroll and His approach will be visible to all. Jesus still comes as a thief, because it will be a surprise, but the events that need to take place require a heads up of some kind, so there is time for the prophesied reactions to happen; again, everyone from a king to a common man will require time to react as per prophecy, hiding, moving to the mountains and dens, etc. Thus, my conclusion is that Jesus will be seen coming for some time in the sky before He actually arrives and every eye will see Him.
I would also point to Life Sketches 66,67 and/or Heaven (2003) 47.2 as possible insight into the time frame of His approach.
Of course, I could be wrong, but it makes sense to me.