pugsville - In a sense that is right, and it is why the British rulers kicked out the imperial administration in 410
It was 400 AD actually (410 was the year Rome was sacked by Alaric). And the Romans voluntarily withdrew, they were certainly not kicked out. In fact, all the evidence suggest that the British elite regarded the Roman withdrawal as a disaster. And subsequent events proved them right.
but behind that is the fact that Britain at that time had suffered less from invasions than Gaul and Spain
True, but they were soon to make up for lost time....
and was rich enough to make these bids for imperial power possible (Constantine had achieved it, after all).
Only so long as it was part of the Roman Empire. When the legions pulled out, the economy was fucked.
But for the plague in the mid-sixth century Britannia would have been the first successful post-colonial Roman state and preserved Roman civilization in the West.
Britain had already suffered successive waves of barbarian raids well before the plague of the 6th century. Things had actually got so bad by then that the British ruling elite had invited Saxon mercenaries to migrate here with their families in order to defend them. We all know how that ended....
In fact the cultural centre moved to Ireland. You can't win 'em all!
Indeed. But of course Ireland suffered less disruption than Britain during the collapse of Roman administration, since it had never been part of the Roman Empire in the first place.
"Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies." - Marx (Groucho)