Ultimately, the dollar is backed by US military force.
Historically, atremps to debase markets from US dollars have been met with military intervention (khadafi et al). This enforces a relationship between dollar value and global resource value.
The US military is so vast that it has no legitimate challenger on any strategic scale, and nuclear deterrent is traditionally irrelevant to this type of threat model.
Lets imagine. All of a sudden, China has decided that USD SWIFT payments are no longer acceptable, and requires all exports to be settled in physical gold.
Suddenly, the vast majority of consumers are no longer able to buy goods from China, as the vast majority of consumers do not posses physical gold. Those that do, do not have gold in small denominations, and now costs have to round up to whatever denominations of gold that one has. How do you buy things with $400 sovereigns and $1800 kugerands and still make change?
So instead, we now rely on the banking industry to magically transport this problem away. We still pay USD, and it's transparently converted to AU for you in the background. The banks pool enough transactions together, and do T+2 settlement. Except due to the trade deficit, outflows are going to be significantly higher than inflows, and the vendors would rather have the physical gold delivered before issueing the products, given that massive trade deficit.
So now the banks need to arrange for regular, and large transports of physical gold. They also need to do this securely, since gold is a tempting target for theives. Shipping by air is too expensive, and few people will be willing to face transaction fees that high, so then it returns to sea freight, which is slow. Suddenly T+2 settlement becomes T+50.
So now you're waiting 50 days for your $5 payment to clear, before goods ship, which take another 2-5 weeks depending on shipping method.
Or you'd just buy from someone else, who's willing to settle in cash.
To get a transaction cleared inside the next block today costs 185 satoshis per byte, and a minimum transaction size of 192 bytes. So "almost instant" clearing (~10 mins if you're happy to accept one block, ~30 mins if you're waiting 3 blocks, etc) costs a minimum of $18 today.
So that $5 tee that takes 30-60 mins for payment to clear just cost you $23.
As the rate of transactions wants to go up, the cost to get into the next block will go up too. We're already at maximum transaction rate, so the only mechanism left is increasing the price.
Or you could buy local.
(Inb4lightningnetwork)