To what degree does a threat to a nation's humanity pose an existential Risk?

How can we improve the situation in resource-limited settings and change the global approach to allocating resources for research and public health in these areas? Toby Ord highlights in 'The Precipice' that even current dangers are not adequately addressed in poorer countries, leaving them vulnerable to outbreaks. How does this vulnerability connect to the overall risk a nation faces when its public health is underfunded, potentially posing an existential threat to its humanity?

To what degree does a threat to a nation's humanity pose an existential risk?