is slowly dying. Japan is 1.30. China is 1.16. Even Vietnam is 1.94 and falling quickly. These countries aren't far behind Korea.
The same is true of Western Europe and North America. The US is 1.66 and falling. The Netherlands is 1.62. Germany is 1.58. Nearly every country in Western Europe is below replacement rates.
Just about every developed nation on the planet is experiencing the same thing to some degree. Even India is now below replacement rates and falling quickly.
There are definitely cultural and other factors that contribute to fertility rates, but it's a largely biological phenomenon. John B. Calhoun's groundbreaking research at The National Institute of Mental Health in the 1960's and 1970's predicted precisely what's happening now in the overcrowded and generationally urbanized developed world. His work explains a host of other problematic social issues that we're currently experiencing as well. If you want to be depressed, look into Calhoun's work and what it could mean for humanity going forward. What Korea and the rest of the developed world is experiencing is almost certainly what he referred to as "behavioral sink". Google that term. Look into "Universe 25" as well.