The 1944 Breton Woods agreement solidified the US dollar as the reserve currency. It is still used as a medium of exchange for the vast majority of international trade.

The reasons you state: endless wars, income inequality are symptoms of a nation nearing the end of its dominance but not a reason why other countries stop using its currency as the medium of exchange for international trade and commodity pricing. Lots of countries hated Great Britain during their reign and the Dutch during theirs but they still used the British Pound and Dutch Gilder for international trade.

For a country to displace the United States, they’d need considerable economic clout, a well-developed and fair legal system, solid capital markets and banking system that abides by international norms, and a stable free-floating currency.