I read all seven volumes of Gibbon's Decline and Fall of the Roman Empire but understanding the forces behind what transpired remained illusive. Like not feeling satisfied after a large and skilfully prepared feast -- strange. A comprehensive and beautiful book, Late Antiquity, an encyclopedia of articles approaching the vast subject of the Mediterranean/Near Eastern world of 400 - 1000 A.D., provided much more insight by covering social mores, religion colliding with politics, social history and especially economics, a discipline not very well developed (I sure won't call it a science) during Gibbon's era.
Believe it or not, a series of historical novels by the author of The Thorn Birds helped immeasurably in pulling all of this together into a synthesis that worked. If there is a college course that ranges this widely to make a complex subject come into focus, I'd like to hear about it.
The Rule of Empires, recently published, states the theory that had seemed most plausible to me after plowing through all the above sources: empires are created by looting the wealth and exploiting the labor of conquered peoples, and die due to a fatal contradiction which causes the financial basis of the empire to crumble away. That is, stable rule requires the cooperation and assimilation of imperial subjects which makes it progressively harder to profitably exploit them. After confiscating the gold of the Celts in Gaul (who had excelled in mining) and the Jews (70 AD), and enjoying a huge regular income extending back to the days of the Republic by selling millions into slavery, the balance sheet for the Romans reversed itself: the subjects of the empire were now citizens with rights (unthinkable during the heady days of the expanding Republic) who cost a lot to protect and maintain and whose wealth remained more local. The modern Belgians, under King Leopold, were cruelly smart: after brutally robbing the Congo, they just left -- no maintenance costs. The French followed the empire model instead, trying to hold on to the rubber plantations of IndoChina as well as North Africa (were date palms and cheap wine that important?) after World War II. Predictable results.
Dmitri Orlov (website: club orlov) observes the striking similarities between the collapse of the Soviet empire and our path to that same fate: delusional self-image, inflexibile ideology, and an unresponsive political system which even while intact is essentially paralyzed. Being much more highly developed, complex and energy-dependent, however, we have much farther to fall and will incur even more damage.
On the lighter side of history, how about we dig out some Historical Fun Facts? In the pine woods of southern Mississippi, there was once, sort of, a Free State of Jones. A Woodstock Nation/Petticoat Junction for 19th century rural folks, who much preferred doing their own thing their own way. Around 1830, Jones County was depopulated when former Choctaw lands to the north and vast stretches of Texas were opened for settlement. When county officials were at the end of their terms, the positions stayed vacant; there was no crime and no courts were held. In this poor but happy utopia, the few residents there were went to church barefoot and carried their muskets everywhere in case there was some tasty wild game passing by. With no plantations or slaves to defend, they were largely against secession, even though three companies of Confederates were raised (probably just because some excitement was in the offing). Many, however, deserted and came back home. One Jasper Collins said he "did not propose to fight for rich men who were at home having a good time." Confederate conscription policies were lenient on planters, manufacturers and the connected (remind you of the 1960s instead of the 1860s ?). Captain Newton Knight organized a group of anti-Rebel rebels with headquarters on a river island in late 1862, which conducted raids on the Southern forces and fought three battles with them. Jones County had more or less seceded from Mississippi and the Confederacy, and after the war was not bothered by carpetbagging (there was nothing to steal) or Reconstruction policies (few ex-slaves). The state changed the name of the county and its seat to Davis and Lee, respectively, in revenge, but that was undone in 1869.
So let us raise a jar of white lightning to the independent rascals of the Free State of Jones, who were far wiser, and a lot more fun to hang with, than the murderous mavens of empire.