I think the crux of our disagreement here seems to be that you believe size is the main driver of Rome's failure and complexity should play no (causative) role.

I think the crux of our disagreement here seems to be that you believe size is the main driver of Rome's failure and complexity should play no (causative) role. I have a more nuanced position: size was certainly a strong causative factor, but it had an intricate relationship to social, military, other complexities in a strong feedback loop that took place over centuries. In large, complex systems, it's never one factor that fully causes another, but a complex feedback occurs; sometimes the system tends towards homeostasis, while other times a feedback occurs that utterly transforms the system as a whole. Let's just talk about Rome in particular. Rome's Empire has often been called the 'accidental' empire in the sense that the Roman Republic and the people did not seek out to create an empire from the get-go, but it sort of fell into their lap. How did this happen? 1. Rome was embroiled with constant conflicts with their neighbors starting with the Etruscans and Samnites and developed the military and social institutions (a certain form of complexity here) that let them eventually triumph 2. To defeat their enemies, Rome eventually built a massive war machine (complexity) and found out that conquest was very profitable (selling slaves back in Rome, pillaging and taxing the conquered territories—tons of social, economic, and military complexity, but here have the beginnings of size as well). 3. However, this 'pillaging economy' only worked as long as Rome was able to keep conquering weaker neighbors and taking its population as slaves. At any point in the process, Rome theoretically could have disbanded (or drastically reduced) the size of its legions and decided 'here is enough', but internal conflicts, the quest for glory, etc. kept the military adventurism, because it was profitable for the generals and troops that lead the conquest (a complex arrangement, leading to 'size') 4. Administering a vast empire was difficult, so simplifying reforms (which, as you say and I completely admit, may reduce complexity) like standardization of coinage, law, military equipment, etc. occurred in the late Empire. However this was still in the context of an overly bloated (size) and overly inefficient (complexity) Empire that was only held together by military force So I think you're absolutely right if your thesis is that size -> complexity. However, in certain cases (like Rome's), complexity -> size as well, and the combination is key. And the rise and fall of Rome over the centuries can be seen as a certain path one can take: initial complexity (the highly profitable, 'accidental' Roman war machine) -> overly fast, unsustainable growth -> forced additional complexity due to size -> failure to reform (and simplify) quickly enough -> collapse