"All any other country can really do is become the next hegemon"
I think world history disagrees. Europe fractured for centuries and only with the industrial revolution created large centralized states.
Hegemony requires an advantage - the conqueror enjoys some superiority of mobility, usually due to a technological or productive advantage of some kind. For example mongol stirrups or US WW2 tank production.
This allows large empires to quickly form.
But most of history involves defensive and attrition assets that are more cost-effective than mobility assets, especially once we get the widespread adoption of gunpowder. Virtually every peer conflict since the US civil war - except the Western Front of WW2 - has been decided by attrition. Even WW2 was largely decided by industrial attrition in the East (supported by USA), enabling the Allies to rapidly sweep through France & Germany. WW1 and Russia/Ukraine are prime examples of industrial attrition wars. Arguably US wars in Vietnam, Korea, and Afghanistan are as well, and those aren't really against peers.
Now a multimillion-dollar plane can be destroyed by a Stinger missile costing a few thousand dollars. A multimillion-dollar tank can be destroyed by a Javelin missile costing tens of thousands of dollars. Artillery can be linked to satellite surveillance to rapidly target oncoming equipment. Submarines can operate relatively freely, but surface vessels can be targeted and destroyed.
I think we will not see western WW2-style rapid mobilized conquest in the near future.
If defense is more cost-effective than offense, and if one country doesn't enjoy an enormous technological or industrial advantage, empires won't (generally) grow. Instead they will fragment over time.
With globalization industrial capacity is much more widespread. Much of the manufactured goods consumed in the US are produced in China, Mexico, S. Korea, Vietnam, Indonesia, and other places. Technology is certainly not uniform but as the recent Hauwei/SMIC 7nm chip shows, the Western monopoly is far from perfect.
I do think it's possible we might have another country achieve world domination temporarily - especially with technological or industrial breakthroughs. But I am convinced the long run trend is towards trade rather than war, because it is more productive & conducive to long-run technological progress, which is a major factor in winning wars in the first place.
