For instance "The Decline of ..." compared with "A Decline of ..." present really different scenarios, one ultimate and one incremental.
In 1955 John T. Flynn wrote a book about American decline, which paints a different picture when compared to the picture that oral histories and traditions of Native Americans paint about American decline, even though both deal with the same subject matter.
Authors sometimes see "decline" as a form of how events are adversely effecting their own lives, and therefore, what is really being described is an author's perception of what is happening near them.
Thus, one can read two works and wonder if the authors were both talking about the same nation, continent, or even the same planet.
After looking at some of these "declines" of this and that, I notice that much of it is simply another way of saying "there goes the neighborhood".
The literary work ends up being someone projecting their own bias and prejudice into some subject matter, rather than being a comprehensive diagnosis of the decline of an empire or nation.
Getting back to Flynn, one thing is for sure, he was not afraid to write dramatically:
I lay it down, therefore, as a proposition susceptible of complete proof, that our difficulties do not have their origin in the struggle with Russia or our massive debt and oppressive taxes squandered all over the world. These are the external and visible symptoms of our illness. America is sick. OUR basic disease is that WE HAVE ABANDONED THE AMERICAN SYSTEM OF GOVERNMENT. We have dismantled the American Republic and reconstructed it on an alien and corrupt plan.(The Decline of the American Republic, page 4, PDF). He considered his thesis "susceptible of complete proof", which might be seen as an attempt to put the "science" in "political science", but that dogmatic assertion would also surely generate skepticism.
Hey, are you tempted to wonder if one man's "decline" is another man's "ascension" as I have been?
Perhaps that notion is what one author meant when he said:
"This is not a book about the decline of America, but rather about the rise of everyone else."(The Post-American World, by Fareed Zakaria). I think we have to admit that Mr. Zakaria has learned much after immigrating to the U.S. from India, especially how to spin softly but write a big book.
Getting back to the subject "a decline or the decline", a classic example to consider is the Roman Empire.
That empire's decline is attributed to a whole host of causes by a whole host of historians.
Wikipedia has some text containing an example which might indicate that all declines have multiple "a declines", but only one "the decline" in the final analysis:
... decline of the Roman Empire refers to both the gradual disintegration of the economy of Rome and the barbarian invasions that were its final doom.(Wikipedia, bold in original). In refined terms, the final doom of an empire is "the decline", while incremental disintegrations preceding that final doom are a series of "a decline" events.
I once compared this to the phases of an urbanite freezing to death, and the very perplexing and practically universal human behavior phenomenon of the taking off of the clothes in the final phase of freezing to death.
Who in their right mind would take off their clothes while freezing? Well, that leads to the crux of the matter.
My offer in this matter is that the one thing that is prevalent in all "the declines" is the ingredient of the institutionalization of delusion.
In the final analysis, once delusion becomes institutionalized, "the decline" is assured even when preceded by "a decline" after "a decline".