What do you think would happen if the USA announced the invalidation of Treasury Securities?

Since the US is an import nation, it would be advisable to forbid all trade towards the US.
Let them starve.

Five simple words: shit would hit the fan.

People (and by people I mean large corporations, governements and incredibly the wealthy) would stop investing in the US. Government bonds are popular because the return is guaranteed if you take that away then there is no reason to invest. Bear in mind that the US issued these bonds because they needed the cash and will porbably need more cash in the future so they need to keep the people who are investing happy. Would countries go to war to get their cash back, probably not.

China would have our asses in a sling. Don’t they own most of those T-bills?

@aprilsimnel China is the largest foreign holder of Treasury securities, followed closely by Japan. See the list here.

Well speaking as an Englishman, I see the UK is in bronze medal position. I’d say we’d more than likely pound/£ the yankee arse.

Everyone on SSI would immediately lose all their retirement benefits. All those PO’d senior citizens would make short work of the duly elected representatives that just threw them under the bus.