In Revelation chapter 6, the first 6 seals on the 7-sealed scroll are opened by the Lord Jesus one-by-one.  NOTE:  It is the Lamb Who opens the seals, which means the Tribulation is not a time initiated by either man's wrath or Satan's wrath!  It is a time of God's wrath on Satan's earthly domain.]

The first 4 seals introduce the judgments of what is commonly called, "The Four Horsemen of the Apocalypse (the "unveiling" or the "revelation").  When Christ opened the first seal, John (seeing into the future) heard "the noise of thunder," which symbolizes coming judgement.  Soon he saw a rider on a white horse, going forth conquering!  He pictures the yet-future Antichrist!  Shortly after his appearance, there is a rider on a red horse, which symbolized blood and warfare.  Then there is a rider upon a black horse, which pictures great famine.  He is followed by the rider on a sickly pale-green horse, who pictures death and Hell follows.

If you think things are bad now, you haven't seen anything yet!  This is why it is so important to come to Christ TODAY; the sound of thundering hoofbeats is just off in the near distance!