In English history, the Viking era dates from 793, when the monastery at Lindisfarne was looted, to 1066, when the kings of England, Norway and Normandy battled for the English throne. Here is a brief introduction, emphasizing the economic aspect:
And this "Normandy" became an all-weather base for Viking attacks on the rest of the Frankish empire [the seas between France and Scandinavia had not permitted winter raiding].
... the fight for control of England continued for centuries. The English were able to regain all lands lost to the Vikings by 954. During this time, the Scandinavian warriors terrorized England and demanded danegeld, payment to ensure peace.
[...] Suffering devastating Viking raids, Charles the Simple, a Frankish king, in desperation offered the Vikings a land grant north of his kingdom. This area became known as Normandy.
Cambridge University Press has posted the introduction to Viking Empires by Forte, Oram and Pedersen. We turn there for an explanation of the start of this era:
The seventh and eighth centuries witnessed a simultaneous professionalisation of the military and a decreased military activity... The relative peacefulness safeguarded by the successful fortification of southern Scandinavia, combined with the improvements in the design of ships, allowed the Scandinavians to re-focus their attention overseas and become what we now call ‘Vikings’.Scandinavia itself had reached a near equilibrium; its own towns were adequately protected by fortification and the credible threat of retaliation. The Vikings are precisely those Scandinavians who sought softer targets elsewhere.
The Vikings' paganism glorified violence and war
In Valhalla, the great hall of Odin in the afterworld, fallen warriors were rewarded with all the meat and drink they wanted, and they could do eternal battle but never die.in what we might today call a death cult:
And they asked his slave girls: "Who wants to die with him?" One girl said yes, and I looked at her, and she looked completely confused. An old woman that was called the Angel of Death now forced the slave girl into the tent where her master lay. The men outside started beating their sticks on their shields so that the sound of her screaming would not be heard, lest the other girls be too frightened to seek death with their masters.
The conversion of Scandinavia to Christianity may or may not have been rapid, but it is certain that Harald Bluetooth of Denmark converted in 965 and Olof Skötkonung of Sweden around 995. Forte, Oram and Pedersen summarize the end of the Viking era:
... its end came about as a slow process of acculturation and integration of the Scandinavian kingdoms into the wider body politic of European Christendom. The Christianisation of Scandinavia in the tenth century brought the area to the attention of the Western Church and the Holy Roman Empire. The Scandinavian kingdoms were subject to the archdiocese of Hamburg-Bremen from the time of the earliest missions in the early ninth century. Therefore, tenth- and eleventh-century Scandinavian kings traditionally regarded as Vikings, such as Svein Forkbeard and his son Canute, both kings of England and Denmark/Norway, were major players in European politics and clearly saw themselves as such. They were not aware of themselves as Scandinavians; nor did they seek to impose specifically Scandinavian customs or institutions on the peoples they conquered.In this view, the conversion of the Scandinavians to Christianity did not itself pacify them, but it enabled or accelerated the cultural assimilation which did. However, contemporaneous with the conversion was a change in the Vikings' methods, from raids and extortion of danegeld to more orthodox wars for territory.