The Decay of Roman Britain - Britain "Independence"

Roman rule in Britain began to deteriorate by constant civil war and barbaric uprisings that were occurring under Roman control in Europe. The Senate of the Western Roman Empire was at civil war with Flavius Stilicho, who had taken control of the Western empire after Emperor Theodosius had died. Stilicho was initially successful against Saxons and Scots who threatened his rule in Britain, but conflict elsewhere caused him to draw troops from inside of Britain and post them other places in Europe. Coinage in mass amounts to Britain was halted in 402, evidence of troop withdrawal from England. Barbarians that looked to take control in England could not be dealt with due to the Western Empire's conflicts with Goths and other barbarians in Gaul.

Usurpers in modern-day France (Gaul) and Spain took control and were, for a short period of time, officially recognized (possibly by threat) by one of the Western Emperors, Flavius Honorius. In an attempt to retake and defend these areas, garrisons in Britain were reduced. When Constantine III was named emperor by his troops it was the last time Britain would experienced the effects of outside imperial rule. When a large portion of Constantine III's troops were absent in Spain in 408, barbarian attacks forced him to withdraw even more troops from Britain, and eventually he was unable to handle the attacks of barbarians in England. Roman rule was finally ended in England was the Constantine's administration was expelled from Britain, followed by similar events taking place in Gaul. Eventually Constantine, with his troops crossed the English Channel into Europe and Roman administrative power in Britain was effectively ended.

By the time the influence of Rome had left the Island of Britain, the culture of the British had decayed by a large standard. Industries had been disrupted by a war that had occurred between Roman legions and invaders of Britain in 367 AD. Pottery, one of Britain's largest industries at the time, came to an abrupt halt at the departure from Roman control. After becoming rare in 400, coinage goes completely out of regular use by 420 in post-Roman Britain. After the control of Rome, different parts of Britain were ruled by usurpers, outsiders that had illegally seized power. One after another, from different backgrounds from Roman military men to indigenous barbarians, often seized control forcefully but at other times were often invited to take power. By 370 AD pagan religious and ritual sites had all but disappeared, and many of the few remaining sites had been converted into Christian sites by the Romans before they had left. A Roman bishop, St. Germanus, wrote of the deteriorating circumstances in Britain after he visited Britain a second time. Originally coming in 429, dressed in magnificent, he tried to spread the word of Christianity. When he revisited in 446, he saw the dissolution of British-Roman culture that had survived at least until the last 430s.

Sources:

Class lecture

The Oxford History of Britain, edited by Kenneth O. Morgan