Please help! ! Come on, awesome! How big was Britain's politics, people's livelihood and population in the 5th century (that is, the period of King Arthur)?

Britain was not very detailed at that time, and there was a sentence on the list of events: in the 4th and 5th centuries, the Roman Empire gradually declined and gradually gave up its control over Britain. The Romans began to withdraw their troops in 407, and all of them withdrew in 442, ending their 400-year rule in Britain.

Whether King Arthur really exists in history is still controversial. Historians who disagree believe that, just like Caesar in Rome, Muhammad in Arabia and Genghis Khan in Mongolia, assuming that King Arthur is a great king who established an independent and powerful British kingdom, such a glorious name cannot be passed down to future generations unless it becomes a cultural relic. Just because there is no objective existence corresponding to King Arthur, the authenticity of the legend of King Arthur is doubtful. But even so, it seems to be a hundred times more difficult to deny the truth of the legendary story of King Arthur and his knights of the Round Table that has been circulating for nearly a thousand years than to prove it. The research and controversy about the existence of King Arthur has been going on for hundreds of years, so far no one can give overwhelming evidence.