Reserve currencies come and go. They usually go because the nation that issues the reserve currency abuses the situation. Delusions of world domination, endless wars and endless welfare are embraced. These terrible ideas are then financed by money that's created out-of-thin-air. This can go on for awhile, and it usually does, but only until the rest of the world refuses to go along anymore. The U.S. fell into the empire trap a century ago, and the world is starting to say: "That's enough."