Increasing supply of USD doesn't mean it will depreciate, especially if demand increase at a higher rate. Demand is increasing because investors have a long held belief that USD is a stable and safe currency during global economic crisis, among other reasons. Hence why USD strengthening even when US has depression level unemployment.
What can potentially destroy the USD, is when people lose trust in the USD or treasuries as a safe haven (which represent USD indirectly because it's repayment is in USD).
-default on US debt to punish China economically
-destabilizing political crisis on the scale of a civil war (ie. military coup in November, canceling election)
-supply side shocks that cause mass inflation (ie.going to nuclear war with China)
-an alternative asset emerges that is liquid, holds value and is accepted globally (ie. Libra)
What you've written is accurate, but isn't relevant to the prior discussion.
I mentioned that printing money makes the US dollar less attractive.
Of course, others are also printing money (to a lesser or greater degree), so their currencies are also becoming less attractive.
But this is a short-term viewpoint, and the prior context was some point in the far future, when the Chinese economy is 2-3x the size of the USA.
Remember that:
1. the the US dollar is regarded as the reserve currency
2. the US has a persistent and large trade deficit
3. the US has a significantly negative "international investment position" - where it owes the rest of the world more in terms of financial liabilities
4. the US has a persistent and large federal spending deficit
5. There is a large and growing federal debt
So if the US government continues to print money, and run large government and trade deficits, eventually everyone will see that the debts and payments will be unsustainable. That would be the US Dollar losing the trust of the market.
So you don't actually need a significant crisis or alternative to emerge, as you put it.
The US just has to continue running large trade deficits which continue to increase how much the USA owes to the rest of the world.
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The Eurozone and China are also economic blocs that already rival the USA in terms of size.
But the difference is that both these currency areas have small trade surpluses.
That means they do not rely on foreign currency inflows to fund their government spending deficits.