Sounds like a question for Oswald Spengler of "Der Untergang des Abendlandes" fame.
Actually, I should expound upon that statement.
It is simple. Every civilisation goes through a life cycle. Birth, childhood, adulthood, and ultimately death. It's just a normal cycle that every civilisation or culture goes through. The paradigm outlives its usefulness. And it isn't just the West - it's the East too.
Largely, according to Spengler in "The Decline of The West" (Der Untergang des Abendlandes), all civilisations reach a point of crisis in terms of its survival and is forced to revert to "Caesarism" (totalitarian rule by the Executive branch of any given government) in order to attempt to survive. This happened in Tsarist Russia, Spain under Franco, Germany under the Nazis, China under the Communists, Japan in the Imperial Era leading up to WWII, for some prime examples.
Here's a good synopsis of Spengler's analysis of the decline of the West (and you will notice that it applies to not only the West as the rest of the world is further down the tubes than the West:
https://en.wikipedia.org/wiki/Oswald_Spengler
Spengler's book "https://en.wikipedia.org/wiki/Oswald_Spengler" is in print in many languages and should be in any good public library's collection. It is a tedious read, but well worth the reading. It will change your entire perspective on History and the World. It's about 300 pages long, but it is an education in and of itself.
Also, if you can find it, read the book or find tapes of the TV series "The Power of Myth" by Joseph Campbell. That too is an education in an of itself and well worth the read/viewing. It explains it all.
In a nutshell, Western civilisation is just at the point the Romans were when the Barbarian Invasions destroyed Rome. If you want to see a dying civilisation, just look for the Civilisation in which its various nation-states refuse to enforce their own borders and respective cultures. When a civilisation comprising of different national entities loses its will to survive, it is manifested in the form of not enforcing national sovereignty, borders and cultural integrity. Essentially, if you refuse to maintain your culture and insist upon not requiring acculturation and assimilation, you are toast in a generation or less.
The message Spengler sends is that no nation or empire in history has ever survived "multi-culturalism' and 'multi-lingualism'. If the culture of a civilisation/nation/etc. refuses to obey the mythology and ethos which informs it, it dies, and dies quickly.
It's sort of like the people who want to eliminate and abolish and illegalise religion for one reason or another - they are intentionally destroying the very ethos and morality which informs a given culture or society. Friedrich Nietzsche had a lot to say about this subject and put it best in his quote: "Be careful in that casting out one's demons that one does not cast out what is best in oneself."
Yeah, I know, TMI.