The premise of inevitability and invincibility of US dollar as reserve currency rests on non-violability of BRICS or other currencies to be global reserve currency. Why does world need global currency or global reserve in the first place? It has never existed in the history of world, and kingdoms were still able to trade bilaterally, In a multi-polar world, nations will find ways to trade bilaterally and regionally by creating bilateral and regional arrangements. Resourceful nations will try to become self-sufficient so they would need only minimal international trade to meet their domestic needs. More nations are going to reject globalism and global trade, and they are heading in that direction
It never existed before because nations (and certainly not private corporations) didn't conduct financial transactions of anywhere near the order of magnitude of modern transactions (not even in relative terms).
And even when they did conduct large transactions (still miniscule in comparison with modern-day transactions - see above), they didn't use fiat currency. (Well, debased specie did eventually come into circulation, but...)
Instead, they bartered (e.g., slaves for land, wheat for olive oil, etc.) - with all the concomitant inefficiencies.
We need a large-volume currency (a.k.a. global reserve currency) because it would be economically inefficient to do otherwise.
Imagine, if you will, a small, isolated town where the only currency is I.O.U.s that anyone can write up in his own name. Some "regular joe" wants to purchase a plot of land from you. Question: Would you rather accept the I.O.U.s of this "rando" - or the bonafide I.O.U.s of the town's "Mr. Potter" or "Miss Gulch" character, who controls half the county?
Or suppose you're a simple grocer: Would you rather that your 400 regular customers EACH pay with their own individual I.O.U.s? (Imagine what your bookkeeping would look like!) Or with the single currency of the I.O.U.s of the local "Bill Gates?"
Regards,
At the link I posted in #31, there is a chart depicting reserve currencies back to 1400.