For many years, gold was the only real currency. The British had a gold guinea and paper guineas, but one could always exchange a paper guinea for a gold guinea. The Germans had a gold mark. The US dollar, well, actually a US $20 bill could be exchanged for gold.
Then came WWI, and Germany lost, and had to hand over all German gold as war reparations, so the mark became worthless, and we heard many stories like the German who sold a home, put the marks from the sale of the home in the bank, and got a cheque for his deposit in the mail since the value was too small for an account, and the cheque was for less than the cost of the stamp on the envelope.
With all the German gold, the UK and French currencies could still be redeemed for gold, but then came WWII: France lost in 1940, and the French franc became almost worthless.
The UK won, but had spent so much on the war they could no longer redeem UK currency for gold, so the £ left the ranks of the Great Currencies.
But the US could still redeem US$35 for gold, so Bretton-Woods made the US$ the world Key Currency: Anyone not a US citizen or permanent resident could redeem US dollars for gold (US citizens were legally not allowed to own gold). The world used the US$ for international trade. Even the USSR accumulated lots of US$ to use for international trade.
Until 1971, when President Nixon said the US would no longer redeem US dollars with gold, and the value of the US dollar fell, but not all that much, since the US$ remained (and remains) the World Key Currency, a fact the evil enemies of the US would like to fix. But those enemies of the US not only don't know what to do about the US$, they somehow remain restrained by Bretton-Woods even though the basis of Bretton-Woods was that the US$ was the only currency that could be redeemed for gold, which is no longer true, but the US$ still remains the world's only Key Currency (of course, as the US government spend $trillions more each year than they take in as income, Faith in the Dollar is not what it once was).
The many enemies of the US can scream all they want, but the US$ remains the Key Currency, even though it can no longer be redeemed for gold, but the US still control SWIFT, and the easiest way to do international trade is to use SWIFT and the US$, and since that is such a popular and useful system, the US weaponised it, and made it difficult for nations to do international trade without SWIFT and the US$.
So the evil Chinese and Russians are desperately looking for some way to create alternatives to SWIFT that are not controlled by the US.
If one reads US analysts, it will be impossible to create an alternative to SWIFT, because SWIFT is too entrenched in global trade.
If one reads Russian/Chinese/Iranian sources, an alternative to SWIFT is coming 'very soon now'.