While Revelation Chapter 6 itself speaks of the initial 6 seal judgments of the Tribulation, it is also believed by some to tell of a time period in which a major conventional war will break out all across the world even though it will be primarily centered in the middle east.  This war will be instigated by the AntiChrist as a means to achieve world domination.  Via this war, as well as the first six seal judgments, one fourth, or 25% of the entire world's population remaining after the Rapture, will die.  This is viewed by many as the 3rd of the great end times wars with Psalm 83 and Ezekiel 38 preceding it.  It is also viewed as the third and final war of judgment against Islam, ultimately destroying it once and for all.  And even though Israel isn't mentioned directly as being at the center of this war, as it is in the prior two, the fact that the book itself focuses almost exclusively on the middle east, and Israel especially, seems to indicate that Israel will indeed be the central focus of the war, or at least a primary participant.