Why is the modern world so diseased - so suicidal?
The root is purpose in life. Justification - that is, why one exists. Traditionally, families would affirm their striving towards the good. That is, towards towards God. This imbued individuals and countries with purpose.
Now though, the modern world believes in no so such thing. It is a zombie, aimless, just consuming while decaying. It knows its own fraud and disease and its attempts at survival are mere minimum. There is no reaching towards Heaven, for they can never acknowledge its existence.
Declining birthrates, population replacement, etc. - symptoms of the disease at the root.