@nprofile1q... "The US buying its own debt will just devalue the currency." -- Against what? I don't see what you're claiming, after indexing the Yen, Euro, and Sterling against the USD, overlaid with the Federal Reserve holdings of Treasuries.
"In order to free up the money to buy yen, Japan has been selling US government bonds – known as treasuries. Many countries own US bonds as a store of national wealth, but when they are sold in large quantities, that can lead to a rise in the interest the US treasury pays on its debt." -- It may, but that's rarely the case. Countries don't just start selling off USD because they want to; they're largely held relative to the Balance of Payments. See how 30-year yields kept going up despite increasing foreign holdings of Treasuries?

