a creditor can trigger it involuntarily by one's insolvency - liabilities bigger than assets. IOW it doesn't take missed payments.t Most of us are insolvent, by that standard, if we had to go "all in". No one cares because we all live day by day, and pay off our debts eventually.
Federal governments are likewise insolvent, except for one asset that trumps (!) it: unlimited taxing power; "the full faith and credit" of the government are behind its bonds e.g. That's how they finance wars.
So bankruptcy and insolvency are irrelevant terms.
If the situation goes on long enough, in historical terms, then the "faith" part is lost and collapse follows. Gibbon says the "Fall" of Rome took from Augustus to Marcus Aurelius, anyway, if not later, at the loss of Europeean colonies.
A problem that existed then but is worse now is overextension. Wars being fought on three fronts: Middle East, Afghanistan, Homeland Security aka antiterrorism. Infrastructure needs, including disaster-related. An alienated 99%, increasingly so. The economists' term "scarce resources" becoming more relevant outside the classroom.
The punchline - you've been waiting for it: Those are some of the problems facing your government, but not mine. Haggai 2:6-9.