You're reading a post from 2011-09-14. I have at best a dim memory of what's written here.
The Decline and Fall of the Roman Empire is the second lecture series I’ve listened to by Thomas Madden. I find him very enjoyable to listen to. These lectures recount events from the end of the Roman republic to the mid sixth century, focusing on the rulers.
The main rough idea I picked up was: the republic collapsed as power started to concentrate in individuals who derived their strength from the loyalty of military legions. Conflicts between such individuals easily led to civil wars; a single person acquiring all the power could allay this, but there was recurring difficulty in making that person’s successor clear.
A fascinating pattern Madden discusses: army A supports X as emperor, and army B supports Y as emperor. Army B decides the battle probably won’t go well for them, so rather than duking it out with A, they just kill Y and accept X. Life as a prospective emperor must have been stressful…