alt Hacker News>The idea that you "need a single extremely powerful country to replace it or the US will stay in its position" just doesn't add up. I'm not fully sure if that is what you meant but I have seen that argument a few times.
The OP goes further than merely claiming that US will lose its spot as the top power. It claims it won't be a world power at all:
>in 50 years America won't be a world power any more. It'll be in a similar place to Canada at best
For reference, Canada ranks #11 in GDP, below Russia and even Brazil. On military spending it ranks #16, below Poland and Spain. It doesn't have nukes. To suggest US will ever come close to that in 50 years is laughable.
> claims it won't be a world power at all:
which is very much possible
50 years once just a blink in human history is today enough to have 2 major industrial revolutions
nukes are not an argument for anything but main land defense from invasions
Look Russia, it was considered on of the most powerful countries military wise and cleanly in the top 10 economically. Many treated it as a 3rd place behind USA/China. It probably will be neither military nor economically overly relevant in 10 years. Through comparing a war economy with peace economies by most normal usable standards (e.g. GDP) isn't very meaningful. Yes it has nukes, no one will invade it (in a traditional large scale sense out side of some border conflict). But it's economy looks like the kind of war economy which leads to a complete economical collapse once the war ends (i.e. burning core substance) end while it's military could be very experienced now, by treating soldiers as highly disposable its unclear how much that actually is true.
Now look at the US, it has lost the majority of soft power thanks to incompetence (and it was maybe the nation with the most effective soft power). It has alienated most of it's allies, especially it's closest allies. Both from a military and economical POV. It's highly dependent on China, and tries to change that have shown very mid to bad outcomes. On the other hand China is increasingly less dependent on it (and the EU) and increasingly less attackable by sea blockades and other non-hot war counter measures the US had. It's behind on automated production. Countries are increasingly less willing to tolerate US bases on their ground which are essential for it being able to project power. The economy is increasingly dependent on a few pillars, which are strong but can crack anyway. The might claim AI leadership, but practically it looks like the price they payed to get there is one which not only will not pay of but can not pay off, it's just way to high. War is also increasingly going back to ways where even if you have superiority the cost of waging it is still severely high, in such a situation you can't force leadership by military force, if you try it likely will end similar to Germany in WW1. Lastly the internal instability Trump has brought by dismantling checks and balances and arbitrary gutting of programs which turned out pretty essential for stability is bad enough to argue things like a putsch series or civil war being _realistic possibilities_ (not guaranteed at all, but possible where it wasn't realistically possible before).
If you put everything together the US dropping temporary out of the top 10 of overall most powerful countries is, not very likely but, very much possible.
It does have absurd geographical advantages, and nukes to make sure it keeps them basically for ever (as long as it doesn't splinter which isn't very likely tbh.). So the drop would be most likely be temporary at most.
Still it is possible, it's the price to pay for first squandering all trust/goodwill gained from WW2 over a few decades of greedy, egoistic, egocentric, ethical catastrophic politics. And then going complete "unpredictable, untrustable, instabile, high risk, publicly considering to start war with NATO or at least half of the EU (JEF+some others)" in recent years.