

In archaeology, you can peg the beginning of an empire’s end when it stops building public architecture, whether it’s art or infrastructure (equal to spending on the public). Once the government stops giving back to the populace, it’s over.
Separate and complex discussion defining “empire” in archaeology without written records, so I am just referring to a particular geographic center exerting cultural and economic influence on its neighbors.
Stop public spending. People move out. Economy declines. Some other political center rises to prominence.
Obviously there are a ton of other factors affecting this, but it’s a broad-brush pattern seen repeated over thousands of years.
I did not mean to imply the cessation of public spending was causal, just indicative. First ran across it studying mesoamerican civilizations, but I think there are academic papers about Eurasian examples as well. Usually the cause is periodic shifts in rainfall patterns, or other environmental factors. This is an ok place to start, but I would have some work to dig up the textbook. https://www.oerproject.com/OER-Materials/OER-Media/HTML-Articles/Origins/Unit5/Cycles-of-Collapse-in-Mesoamerica
Edit: here’s a good paper: https://journals.sagepub.com/doi/10.1177/00420980221105418