Theory: Aging + low TFR regions (e.g., Puerto Rico, Ukraine) = &gt; Vulnerability. 
Major "shocks": hurricanes, wars, recessions = 
&gt;youth emigration, weaken economy, &lt; tax rev, &gt;debt, disrupt family formation &amp; &lt;TFR more etc.
➡️Eroding resilience further. Feedback loop intensifies.