A rise in false religion, including an epidemic of persons or systems claiming to be Jesus Himself.
An unprecedented increase in the number of wars.
An unprecedented increase in natural disasters, including famines, pestilences, and earthquakes.
Unprecedented tribulation and mass martyrdom, and universal hatred of Christians.
Mass betrayal, and General Apostasy.
The Gospel shall be preached to all nations.
The Abomination of Desolation will be set up in the reconstructed Tribulation Temple.
Tribulation so great that there has been none like it before, nor none since; in fact, if the days had not been shortened, no flesh would survive.
An increase in false signs and lying wonders.
Immediately after the Tribulation of those days, there will be great atmospheric/astronomic disturbances.
Coincident with this, the "sign of the Son of Man" will appear in the heavens, and "all tribes of the earth" will see Jesus' mighty Second Advent.
Coincident with this, the saints of God will be gathered together from the four corners of the earth.