Before the 5th century AD, tribes of northern Germanic farmers, such as the Angles, Saxons, Frisians and Jutes, engaged in raiding and piracy around the North Sea lands. After about AD 400 they began migrating into adjacent lands, for many reasons.
Populations were growing but flooding due to increased rainfall was reducing the availability of cultivable land. The evidently declining Roman Empire seemed an easy target.
Some northern groups moved into eastern Gaul, others flooded into Britain. The invaders were generally bands from different tribes, frequently labelled with the tribal name of their leaders. They gained control of areas in south and east England but for several centuries stiff native resistance prevented their conquering the west.
After the initial invasion, the war-bands carved out kingdoms for themselves which grew steadily in size and prosperity. On the continent where they met weak resistance, barbarian groups inherited a Roman administrative system that continued to work smoothly. In Britain, however, prolonged fighting led to the weakening and dilution of Roman culture.
Many Roman towns fell into disuse. Native chiefs who had held the reins of government under the Romans now became petty princes, sometimes welded together against the Germanic threat.
