I'm reading a new anthology called APOCALYPTIC, edited by S. C. Butler and Joshua Palmer. Not surprisingly, the stories tend toward downer endings; optimistic viewpoints on worldwide devastation are few. So far, my favorite piece, "Coafield's Catalog of Available Apocalypse Events," by Seanan McGuire, isn't exactly a story, because it has no narrative arc. It comprises a humorous A to Z list of alternatives offered to customers who have "decided to end the human race and possibly the world," promoted by what appears to be a sort of disaster-scenario catering service. Q, by the way, stands for "Quantum," and Z, of course, represents Zombies.
TVTropes has a page listing all major scenarios for the destruction of the human race, Earth, the solar system, or the universe:Apocalypse How
Disasters are classified according to Scope (all the way from local or city-wide to universal, multiversal, or even omniversal) and Severity (from societal disruption or collapse up to physical or metaphysical annihilation). Examples of each possible permutation are cited, and there's also a list of pages for the most common causes of disruption or destruction.
Back in 1979, Isaac Asimov published A CHOICE OF CATASTROPHES, an exhaustive survey of possible ways our species, our planet, the solar system, or the entire space-time continuum might end or at least become uninhabitable. He categorizes them as catastrophes of the first through the fifth class, from universal down to local. The first class involves the entire universe. Second, the solar system could be (indeed, eventually will be) destroyed or rendered inhospitable to life. Third, life could become impossible on Earth. Fourth, the human species might be wiped out while some other life survives. Fifth, humanity could survive the destruction of our civilization. The fifth class is the type most often portrayed in "apocalyptic" fiction featuring plagues, zombie hordes, meteor bombardments, etc.
I'm not sure how the word "apocalypse," which is simply Greek for "revelation," got its popular meaning as the cataclysmic end of civilization, life, or the world. Most likely the connotation developed that way because what the "apocalyptic" biblical and extra-canonical prophecies usually revealed was the destruction of the present world order and sometimes Earth itself. When Buffy saves the world "a lot" and the Winchester brothers in the SUPERNATURAL series prevent multiple apocalypses, it's life on Earth they're usually saving.
Anyway, an author who wants to destroy civilization, humanity, organic life, the world, or the universe has a plethora of methods to choose from.
Margaret L. CarterCarter's Crypt