Final answer:
The Britons, who were Celtic inhabitants of Britain, were driven into Wales following the Anglo-Saxon invasions by tribes such as the Angles and the Saxons after the Romans left Britain around 400 CE.
Step-by-step explanation:
The settlers of Britain who were ultimately driven out of England into Wales by the invasion of Germanic peoples were the Britons, also known as the Celtic Britons. The invading Germanic tribes which included the Angles and the Saxons came from modern-day southern Denmark and northern Germany. After the departure of the Roman legions around 400 CE, these tribes occupied southern Britain and were referred to as Anglo-Saxons, a term that became common in the eighth century. The native Celtic Britons, having been pushed out by the newcomers, found refuge in Wales, among other places.