The US has a healthy immigration system that brings in a consistent stream of workers and tax payers to support all the old people about to clog social assistance channels for decades. That's the strong trap that Japan has been stuck in for decades, and the one that'll start befalling China in a decade or so. It'll be interesting to see if Japan can escape the population deflation or if this is a constant shrinking population from here on out until it's untenable to continue as-is.