arkA and Wozza, I gotta give you guys credit for imagination in seeing some things in my writing that I, er, didn't actually write. When did I write that Rome was a democracy? It was an oligarchy, of course, that grew more liberal over time.
And, MarkA, I wish you'd try rereading my original comment and first reply to you, because the reply on innovation's and Imperial military ineffectiveness is already in there. Short version: do you think the many Romans hurt, displaced, or in conquered turf saw it your way, much less Attila?
Wozza wrote:
Oh, yes, because the Roman Empire was actually ruled by Martians instead of humans.
Do you live in our timeline?
The Senate was effectively powerless, losing them an important thoughtful group check on executive rule (as you noted). All the institutions were maintained, but all the liberty was taken away. Citizenship was spread wider, but it was easy, because votes only counted for minor posts. And the Early Empire was almost continually on the warpath; though, it was the only period in which it succeeded consistently. Even the early changes of monarchies had unpeaceful bits. And calling Caligula's and Nero's reigns peaceful is IMHO quite the spin.
It's true the Empire lasted much longer; my count is 1500 years because the Byzantines were politically continuous. If that's what you mostly care about, then it did great. Personally, I rate how the people did, individual freedom, and innovation higher. And the Empire was worse at all these than the Republic.