Yep, every powerful nation or empire in the past has collapsed or faded in significance after some time. The question is, in our case, will it be a rapid collapse or a slow fade (like the British empire), and when?
Rome by comparison took 700 years to grow, and 200-plus to collapse
By comparison, when Rome fell apart (which admittedly took some time), the standard of living was objectively much worse for average Romans. They went from a civilization with plumbing, toilets, cities, aqueducts, a Coliseum with water shows, and probably the highest standard of living in the world, and a society with specialization of labor, education, rule of law and a well-developed legal system, to feudalism, where they lived under feudal lords as uneducated serfs living in huts and working in fields. It took over 1000 years for western society to get back to the level of technology and development they had under the Romans.
It would be better to treat the British Empire and the United States as two forms of the same empire, as they both speak the same language The capital of the empire simply moved from London to Washington via an internal revolution, a process that's happened many times in the past, e.g. Lisbon to Rio de Janeiro, St Petersburg to Moscow, Xian to Hangzhou, Kyoto to Tokyo. So the British Empire/United States reached a peak after 400 years, and is now declining for perhaps a few hundred.