I think in some very important sense, the Roman Empire basically died before it was ever an empire, even before Julius Caesar was a guy with popular support, and cause of death was power gravity.
Of course, this is profound oversimplification, and is perhaps justifiably dismissable. This is also playing with the definition of "death" the same way that "you're already dead" said to someone who's about to lose a life-or-death fight with you is, or even the same way as "we're all slowly dying all the time".
In another view, Rome died because it could only succeed as it did by having an inherently unsustainable pattern of feeding itself with unceasing conquest, and it eventually stalled out on all fronts as it reached terrain or peoples that it was unable to sustainably conquer or control, or stretched so far that its communication technology could not keep its parts as one sufficiently cohesive nimble whole.
And then Rome started to gradually falter and fail and weaken, and many complex interconnected failure modes started to express themselves, and the whole thing kinda rattled apart internally while increasingly failing to deal well with external pressures over the course of centuries. Wealth influx flowed, suppression and bribery of conquered and neighboring territories weakened, internal loyalty and cohesion weakened, and each time that boiled over into violence the affected areas faltered or took damage which in turn made those areas contribute less to the health of the empire, and so on.
But the point I'm trying to make is that I think, crucially, if more of the countless people in Rome had a real say in how things were run, if Rome had managed to stay a Republic and improve at being a representative government rather than turning into a dictatorial one, then Rome could've had a better chance at figuring out better solutions.
Instead of tapping the wisdom of the crowd, instead of using the massive distributed parallel processing capabilities inherent in such a large population, instead of listening to the full "sensory" data and "thinking" that the Roman organism had from each of its human "cells", Rome silenced itself, damaged and drugged itself with censorship, punishment, fear, gladiatorial games, a culture and value system favorable to having a dictatorial emperor, and so on. A tiny little piece of the whole Roman "mind" running the whole show, increasingly ignoring the rest, increasingly optimizing for itself with increasingly more willful ignorance and disregard for how that hurts the whole body.
It takes a certain disproportionate concentration of power to ignore or neglect your people's wants and needs. And yes, sometimes, that power is at first willingly given in the form of popular support - Caesar was able to prototype the dictator role because he had popular support - but Caesar only got that popular support because power had already concentrated too much in the ruling class, in the political elite, in the relatively small number of people who got to effectively dominate the Senate.
He had popular support because people under the boot of an entrenched unrepresentative power structure just dig themselves deeper by emotionally resonating with the idea of a single amazing leader who can fix things.
Power gravity had already progressed too far by the time Ceaser came along, he was just the right shape of a person at the right time for the power to get crushed by the gravity onto him, for that much power to undergo the next stage of its collapse. Ceaser's actions sped power gravity along, facilitating the emperor that followed. But the Senate and ruling class sped power gravity along before that.
