The Raid of Lindisfarne is considered to be the dawn of the Viking Age, forever changing Europe. Vikings attacked a defenseless monastery called Lindisfarne, otherwise known as the "Holy Island". During this time, monasteries were undefended due to the holy nature of the site. The Vikings raided and pillaged Lindisfarne, slaughtering the monks which inhabited the Holy Island.
This video by Extra History does an excellent job detailing the impact of the Viking Raid of Lindisfarne.
The Danelaw was an area of England which was colonized by the Vikings during the 9th Century. This area was ruled by Danish Law, rather than Mercian or Northumbrian law. This effective colonization of England had ramifications on the English language itself. Many Englishmen within this region have probable heritage from the Vikings.
It is entirely possible that I may have Nordic Heritage, as my Father's family originates from this region.
An incredibly brief article describing Danelaw.
This is considered many historians to be the final battle which cemented the Viking retreat from Europe. Harold Godwinson decisively defeated the the King of Norway. Shorty after this battle, William the Bastard defeated Harold Godwinson's exhausted troops, cementing himself in history as William the Conqueror.
An animation presenting the last years of the Viking Age in England.