Medieval Invasions of Britain
Medieval England was invaded on several occasions by three different peoples: the Saxons, the Vikings, and the Christians.
The Saxons came from Northern Germany, Denmark, and Holland. They invaded the East and south coasts of Britain many times between AD 450 and 650 for farming land, fresh water, and more land for people to live on.
Viking Invasions
The Vikings came from Norway and Scandinavia. They attacked the north-east coast of Britain. They invaded in AD 793 and then later in AD 1000-1060. The Vikings raided the land of England for many reasons. Primarily, Viking raiders saw the coasts of England as easy targets for looting, as well as rich lands for farming and settlements. Their seafaring expertise, and the very small draft/displacement of their longboats, gave the Vikings unparalleled access to the english countryside via sea.
The Vikings eventually established themselves as a perminant presence in England, establishing the Danelaw.