One of the greatest mistakes made in determining Christ's return comes from these scriptures. The gospel will be preached to all nations. There is an ongoing process where the gospel is preached or bought to all nations and peoples. This doesn't seem right, for when you look at the two scriptures covering this subject, you see it is a one-time event. This is a single event, and Revelations tells us what it is. It has to do with the two witnesses.

Rev 11-7. And when they have finished their testimony, the beast that rises from the bottomless pit will make war on them, conquer them, and kill them, and their dead bodies will lie in the street of the great city that is symbolically called Sodom and Egypt, where their Lord was crucified. For three and a half days, some from the peoples and tribes and languages and nations will gaze at their dead bodies and refuse to let them be placed in a tomb, and those who dwell on the earth will rejoice over them, make merry, and exchange presents because these two prophets had been a torment to those who dwell on the earth. But after three and a half days, a breath of life from God entered them, and they stood up on their feet, and great fear fell on those who saw them. With the advent of mass communication, it is not hard to see this happening. I got some idea of this when I was on holiday on a remote island in Tonga and everyone had smartphones. The event is the death of the two witnesses and their raising from the dead.