History LessonOops. My friend Tim Lee (who does not, to my knowledge, have a blog) informs me that my Roman history below is in error.
Actually, the story I learned was rather different. Most of the wandering into the hinterlands that occurred was in the early years of the empire, from Caesar's conquest of Gaul in the late first century BC to the conquest of Germanic tribes in the first century AD and the conquest of Britain in the second century.Tim later added the following addendum:
When Augustus died in 14 AD, he decreed that the boundaries of the empire should remain as he left them, and with a few minor modifications (Britain being one of the biggest), they did. The Germanic tribes that Augustus failed to conquer were pretty much left alone for the rest of the empire's existence. I believe it was also Augustus who dramatically reduced the Roman military forces by almost half from its peak during the civil wars-- an enormous peace dividend-- and the size of the Roman military was roughly fixed thereafter.
The Romans literally built a giant wall across the continent of Europe, and stationed Roman legions along it. This strategy worked for more than 200 years-- the interior of the empire was more or less safe from marauding invaders from Augustus's death in 14 AD until sometime in the third or fourth century.
According to my history professor, the major causes of the collapse of the empire were internal. First, the Roman government developed a sort of proto-welfare state, which required raising taxes and eventually led to open warfare between tax collectors and wealthy Romans.
Secondly, the Roman legions stationed along the border became more loyal to their local commanders than to the emperor, since many had lived in a particular military outpost for several generations by the third century. As a result, it became increasingly common for a legion to march on Rome to install their commander as emperor. There are periods when Rome got a new emperor every year, each supported by a different regional faction within the army.
Finally, over time the barbarians became more civilized, at least in terms of military tactics and technology. Those closest to the border had the greatest contact with the empire, and so picked up new technologies the quickest. By the time Rome fell, the Germanic tribes just outside of Rome were using essentially the same weapons and tactics as those inside the empire.
When the barbarians finally succeeded in breaching the borders and looting the empire, there was for all intents and purposes no empire left. Rather, there was a patchwork of squabbling factions, with no meaningful control from Rome. At that point, it wouldn't have mattered what Rome had done militarily, because Rome wouldn't have been able to muster much of an army anyway, and they'd have been as likely to turn it on rebellious citizens as invading barbarians.
Most of the German territories were captured under Augustus in 12-9 BC, and Britian was first conquered by Claudius in 43-44 AD. So Rome's borders didn't change much from AD 44 until its fall 300+ years later.Tim asked me to emphasize that he is not an expert on Roman history - but since I haven't taken a single course covering that subject since high school, I'll happily defer to his authority. I don't think this alters the larger point I was making, though. Engaging in unnecessary battles abroad can distract attention from the real threat banging at our door; while that may not have been the Romans' error, I think it's an error nonetheless.