In 383, the usurper Magnus Maximus withdrew troops from northern and western Britain, probably leaving local warlords in charge. Around 410, the Romano-British expelled the magistrates of the usurper Constantine III, ostensibly in response to his failures to use the Roman garrison he had stripped from Britain to protect the island. Roman Emperor Honorius replied to a request for assistance with the Rescript of Honorius, telling the Roman cities to see to their own defence, a tacit acceptance of temporary British self-government. Honorius was fighting a large-scale war in Italy against the Visigoths under their leader Alaric, with Rome itself under siege. No forces could be spared to protect distant Britain. Though it is likely that Honorius expected to regain control over the provinces soon, by the mid-500s Procopius recognised that Britannia was entirely lost to the Romans.
That is from Wikipedia on the end of Roman rule in Britain. I smiled at this sentence, though it does not exactly reflect my view of the current situation:
The Empire’s historical relationship with Germanic tribes was sometimes hostile, at other times cooperative, but ultimately fatal, as it was unable to prevent those tribes from assuming a dominant role in the relationship.
I still think there is a twenty percent chance that the contemporary Brits reverse themselves, starting with inaction and culminating in a new election and referendum. The EU has to “play nasty” in the meantime, but perhaps they too have heard of the Coase theorem. Imagine an equilibrium where each EU nation “leaves,” for purposes of expressive voting, and then shortly thereafter re-enters.
British Parliamentarians and Republican Party delegates need to study up on their coordination games quite soon!