Just as having high income for a long time accrues wealth, existing for a longer time accrues growth.

That would explain why nation states like China and Japan, even though they are smarter than the modern day US, are doing worse than the US. They haven't had as much time to optimize their societies for the area their nation covers and the lifestyles they live.

The US has existed in its current form since 1787 ( Delaware, last state to join the union ). That's 237 years to optimize the same land area.

Modern Japan historically came to be in 1868, which gives it 156 years to optimize itself. Although I would argue that Japan was completely changed after WW2 where they had to surrender their territories that were considered part of the Japanese empire outside of Japan. Which makes it 67 years to optimize itself.

The republic of China was founded in 1912. That's 112 years to optimize itself. However, it took over Tibet in 1951 which is a big enough piece of land to count as a major change in its territory that it has to work over. Which makes it 73 years. 1949 when the Chinese government fled to Taiwan which makes it 75 years.

India gained its independence in 1947. That's 77 years.

Stability leads to growth when it isn't leading to stagnation.

The US is the only place that has had the chance to be stable for as long as it has at its current size.

The fact that even with that large a time gap, the US isn't centuries ahead of the rest of the world suggests that the US has actually been underperforming taking all of its advantages into account.

The modern Chinese state has existed for half as long as the US and already crossed it in terms of PPP GDP.

China has 4x the population of the US, and a higher IQ.

China taking into account that it is half the age of the US, has been growing at a rate of more than 3x compared to the US since its inception to be able to keep up.

Even now the Chinese economy continues to grow at a more rapid rate than the US.

Given enough time the Chinese would obviously outgrow the US, being smarter than them long enough would accumulate the benefits.

The primary challenge that persists for the US is that the population of China is too high compared to that of the US.

The average Chinese is smarter than the average American. The average Chinese needs to be only 1/4th as efficient as the average American to surpass their economy. The Chinese economy is not 1/4th as efficient though, it is far more efficient than that even if not as efficient as the US economy.

China will naturally surpass the US if both the entities maintain their current form, given enough time there is no doubt about that.

The disadvantage over the long run exists for the US as it has to remain 2x more competitive than the Chinese at the end of the century even when taking population loss into account.

Conclusion:

The only solution for the US to remain a future global hegemony is to form a larger union. The average Chinese is well on his way to be more competent than the average European. The US could maintain a 10-15% performance lead over the Chinese into the next century but it is not possible for them to remain two times more productive than the Chinese for that long as the Chinese intellectual competence accumulates over time.

China is guaranteed to overtake the US by 2100 at most if the US does not become an expansionist empire.

Technologically the Chinese are catching up at a speedrun pace.

https://international.la-croix.com/world/objective-moon-china-is-20-to-30-years-behind-the-united-states

Even with all the current disadvantages, we can expect a 1.5x growth advantage in favor of China vs US.

That's easily enough for China to cross the US by the end of the century in terms of nominal GDP.

The US has no choice but to increase immigration and to expand its territories this century to maintain its position as global number 1.

Conclusion 2:

North American Union formed before 2100 to be able to keep ahead of China.