I thought it could lead war, them trying to claim land from america, or just they will no longer wish to give us money. Anyone else have any ideas?
The USA and China are nuclear powers: bringing about nuclear apocalypse would cost China a lot more than lost debt repayments.
Even economic sanctions probably wouldn't be worth it, because China benefits too much from trade with the US.
Everyone would know that the USA couldn't be expected honour financial agreements, so they wouldn't make them in the first place.