Given the countless natural disasters that our ancestors experienced, it is no great mystery that many people fear an abrupt and catastrophic "end of the world" - I think it is in our DNA and collective cultural memory. Think of how often the theme of devastating catastrophe is touched on in popular culture, particularly movies, and the widespread appeal such movies tend to have. I think that religions like JW's attract people (like me) that are particularly sensitive to this fearful strand that runs through our cultural fabric.
Here in the USA, we've had such a good run of relative peace and prosperity that maybe we've come to feel that we're really special. God has blessed the USA I guess you'd say. But, the lord giveth and the lord taketh away. A nuclear meltdown, a terrorist attack, a massive volcano eruption, or a killer disease could wipe out most or all of us in a very short period of time. Enough events like this packed together in a short period of time and across a wide enough area could cause such a complete breakdown of civilization that the remaining humans (if there are any) would likely have to revert back to methods of survival that most humans haven't practiced for millenia.
The following is taken from an article in the New Yorker, I enjoyed the writing. Although the writer is speaking of us as individuals, I think it can be extrapolated to apply to our country, or even the entire world as we know it.
For the lucky few, there is reason to hope that life will be a business of evenly rationed suffering: stern parents perhaps, a few humiliations at school, then a love affair or two gone wrong, maybe a marriage broken. Our parents will die, and farther off, ideally deferred, will come our own steady demise. Plenty of suffering for a life, certainly, but most of us subsist on the plausible expectation that fortune will draw a circle around that personal portion, and that the truly unbearable—murder, rape, dead children, torture, war—will remain outside the cordon. Norman Rush, in his novel “Mortals,” calls this “hellmouth”: “the opening up of the mouth of hell right in front of you, without warning, through no fault of your own.” Without warning, and yet always feared. Job, whom God places into hellmouth to test him, knew that paradox: “For the thing which I greatly feared is come upon me, and that which I was afraid of is come unto me.”