In 397, Stilicho repelled an attack by Picts, Irish and Saxon in Britain.
When marauding invaders attacked Roman strongholds on the continent, Rome (Magnus Maximus in 383, Stilicho in 402, and Constantine III in 407) summoned troops stationed in Britain to fight. In time, the two Roman legions left Britain permanently, leaving the island at the mercy of barbarian attacks. Soon the Britons expelled the remaining Roman officers.
The Pelagian heresy took hold in Britain, in about 420-430, dividing the population into factions. Bishop Germanus was sent to deal with the heresy.
In about 447, under the possible leadership of Germanus, the Britons defeated the Picts and Irish (Scots).
Vortigern gained power in 445. Died in 457.
Unlike the Picts, the Saxons made successful incursions so that the complexion of Britain changed from 450 to 480.