demand is created legal/regulatory environment and open market forces
legal/regulatory environment includes international bilateral agreements and national laws
open market forces influence the evaluation of USD against other currencies and assets
USD is the world's reserve currency, but what does that mean?
for USD to be a reserve currency it must dominate in:
1๏ธโฃ USD-denominated credit issuance (demand)
2๏ธโฃ USD use a means of settlement for payments (liquidity)
this dominance must be at least relative to alternatives