The Romans remained in Britain for about four centuries & during that time Britain was a Roman province governed by Roman governors & protected by Roman legions.
In the 3
centuries the power of the roman Empire gradually weakened. The unproductive labour of the slaves led to the economic decline of the empire. Neither new methods of land cultivation nor new technical inventions were introduced. Slavery became obstacle to technical progress. Poor cultivation exhausted the fields, the harvests became poorer from year to year.
The uninterrupted struggle of the exploited against the slave-owners greatly weakened the Roman Empire too. The enormous number of slaves presented of great danger of the Roman Empire. The end of the 4
century found the Germanic tribes invading the Western Roman Empire & the slaves who hated the Roman state were joining them by the thousand.
Early by the 5
century (407) the Roman legions were recalled from Britain to defend the central provinces of the Roman Empire from the attacks of the barbarian tribes. They didn’t return to Britain, & the Celts were left alone in the land.
During the 5
century the Germanic tribes overran the empire & settled in all parts of it. The fall of the Western Roman Empire meant the end of the slave-owning system in Western Europe.