US is spreading dollars by consumption - import more than you export but pay in USD ..
This leaves surplus USD with exporter ..
Now offer than 4 percent to invest those dollars in buying more T bills .. US debt ..
So the exporter is happy , exporting government is happy ..
China does it in reverse way ..
Export cheap goods to nations .. but ask them to pay in Yuan .. which means they need to hold Yuan .. which means they need to buy Yuan with their own currency ..
The problem occurs when China exports to US .. cuz US won't hold Yuan ..
https://g.co/gemini/share/82280bf91c4d
That is the Crux of the problems.