> One, source? Because plenty of great civilisations across history reached stable states for hundreds if not thousands of years.

Be that as it may. Expansionist empires usually shrinks dramatically once they reached their peak. Both Roman and the British are examples, as well as many Chinese dynasties. The East Roman Empire did survive for much longer so it is also possible for the US to go on for a lot longer. I think the Inca was also kinda stable before the Spanish came.

> And two, America is still expanding. The economy is growing. Post industrialisation, there are more routes to goodies than conquering territory. (I can’t think of a single war of conquest since China annexed Tibet that has gone well for the invader since WWII.)

I do hope that we can drag through this period and make some reformation happen. But I don't have high hope for the current batch of elites. Sure the number is growing.