I think America/Europe would've gone through a similar phenomenon were it not for immigration. Immigration presents a significant challenge to the culture, but it's a necessity to keep evolving the economy and make sure your population/ideas don't stagnate.

I'm from Japan, and I think Japan would've potentially kept it's second place in GDP ranking if they were more aggressive with opening up the country to immigrants and creating a narrative for what it means to be Japanese outside of blood and heritage.