The U.S. dollar is "backed" by threats of violence and ruin against anyone within the land mass called "United States" who disobeys orders given by the mobster rulers who control that land mass.
But that's exactly my point. That threat of violence doesn't
back it at all. It makes it so you need to acquire it at some point, which does give it some value, but it doesn't actually
support that value any more than a 7-11 down the street only accepting USD for munchies supports that value. If the printers were turned on full force, and new USD in circulation was increased by 100% every day, no amount of "threats of violence" will keep the worth of USD from quickly going into the toilet.
In fact, we already have plenty of historical evidence of such. Russian Rubles were backed by their own tax organizations and threats of violence (and Russia had 70 years of practicing
extreme violence), but that didn't help with the backing any when the Ruble went through hyperinflation in the 90' and had to be scrapped. Ditto for any other currency inflated into oblivion. The best the people who have the power to threaten violence could do is watch in despair, along with every other merchant, and wait for some other currency to come along. The only thing that backs it is our collective trust in it (and "our" includes those who can threaten violence, who also have to trust that they can use what they collect to pay those who dole out violence on their behalf).