The period following the Roman withdrawal was one of gradual turmoil and civic breakdown, although St Patrick, writing some ten years after the Roman departure noted that, in the towns at least, some order continued and civil taxes were still being collected and services maintained. The drift was however, towards a return to tribalism with many people leaving the larger towns and returning to the more easily defended hill forts. The power vacuum thus created was to be filled by the Anglo Saxons.
These people were first recorded in 98AD, by the Roman historian Tacitus who describes them as worshippers of the Goddess Nerthus the Earth Mother.
This was no single unstoppable wave of invaders, more of a gradual process. The Romans would doubtless have used these peoples as auxiliaries in their British garrisons and many would have settled in Briton at the end of their service. It would be natural for some of their kin to join them over a period and add to the established settlements.
By the middle of the seventh century Britain was a patchwork of native and invading communities led by powerful chieftains or kings, struggling to gain ascendancy over each other. During this period a small number of kingdoms became dominant, such as Northumbria, Mercia, Wessex, Sussex East Anglia and Kent.
The stronger ones would ever seek to impose their rule and expand territory by force or alliance or by dynastic marriages. By now much of the country was in the hands of the newcomers with the native Britons consigned to the margins.