Quite often people fled with gold to other places, as the countries confiscated gold from people.
US was trusted to hold gold in the world wars, but of course Nixon renegged on the gold standard.
Right now people are starting to hold Bitcoin, and it's much harder to take away from them (flying out with a billion dollars of Bitcoin is trivial, as metal detectors won't catch you), so I'm optimistic that the transition will be more peaceful. Also Bitcoin adoption in US is highe than in other countries.