Question

Why did the romans leave the britons

Answer 1

The end of Roman rule in Britain was the transition from Roman Britain to post-Roman Britain. ... 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.

Answer 2

Following the barbarian crossing of the Rhine in the winter of 406–407, Roman military units in Britain rebelled and proclaimed one of their generals, who happened to be named Constantine, to be the new emperor.