All of the novels have a basic premise; that we are at the end of the present age. Since the novels are Christian fiction, that end is represented throughout the books as my own interpretation of the book of Revelations.
Other cultures had ‘end of the age’ concepts as well. The Norse had Ragnarok; the Mayans had a series of ages called baktuns or cycles which had definitive end dates, many of the Native American tribes had end times prophecies, and the list goes on.
As a species, we are fascinated with our eventual demise it would seem. That isn’t to say that there aren’t real dangers that could end life, as we know it, on this planet. While, for the most part, our world and ecosystem are self-repairing, there is only so much that anything can take. A single giant asteroid, a sudden shift in the tectonic plates causing massive earthquakes and volcanic eruptions, including a super-eruption, or a series of large-scale nuclear accidents could all spell the end for mankind.