"US debt is literally people who have agreed to take US currency in the future and are not themselves part of the US."

I don't think this is true. Foreign holders of US federal debt are only about 6 trillion of 21 trillion[1]. Most of it is held by the government itself or the American public.

[1]http://ticdata.treasury.gov/Publish/mfh.txt

Foreign held debt.

The U.S. used trade agreements to achieve a number of diplomatic outcomes in the post cold-war era, including closeness to Europe and China, to keep Soviet influence down. The Soviet Union doesn't exist anymore though, and China is certainly no longer our ally against them. Europe's economy doesn't need us to provide a one-sided market for their exports anymore to juice their economy either. The purpose of that was to keep them from going red. Putin notwithstanding, that's not very likely anymore.