I think Japan is a case study, as they are a little bit further down the "Fall of Rome" timeline, while also facing the population plateau. They have combated

I think Japan is a case study, as they are a little bit further down the "Fall of Rome" timeline, while also facing the population plateau. They have combated it with a strong national identity, and cultural retention, but time will tell in the next decade how it ends up. 20 years down the line, the Western world, then Africa. China and Islamic countries aren't having this issue, as their (opposite) approach seems to be working in the short term.