Was it because of their defeats by Alfred and the settlement of Normandy? Were there issues at home which changed their focus?
I did search through quite a few of the questions on here, but did not see this addressed.
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A gradual diminishing of the factors that drove vikings to raid, as well as opportunities for successful raiding.
Vikings did not go far from home and risk their lives for the fun of it. There are many theories, and likely many overlapping factors, that caused the beginning of the Viking raids. For example:
Gender imbalance - in a polygynous society, with each man of status expected to have several concubines, there are obviously not going to be enough to go around without raiding.
Economic imbalance - at the beginning of the Viking Age, Scandinavia was not a very rich society. Once maritime technology allowed them to access the wealth of the lands plugged into the Mediterranean system of trade, it was a better way to make money than staying home.
They were successful! A gradual trickle of spoils back to Scandinavia (or settling of "surplus sons" elsewhere in Europe) and the damage inflicted on the economies being raided shifted the economic and gender imbalances closer towards an equilibrium. Raiding became much less necessary.
Integration of the Norse into Christian Europe - Viking chiefs were happy to get wealth without the risk of raiding. They would increasingly be paid off, such as in the case of Sweyn Estridsson or granted rule of European land. Scandinavia would eventually unify itself under three Christian kingdoms, putting an end to warlordism that both created warriors & encouraged them to leave and seek a more peaceful land, relieving the pressure to raid for women, and reducing the acceptability of raiding. As former vikings spread into Europe, they also gained opportunities for a steady salary as part of a mercenary army (this is how the Norman conquest of Sicily began).
Lack of targets - Atlantic coastlines fortified themselves, allowing the wealth of the land to be protected against raiding. Local rulers were able to organize an effective response to viking settlers. Norway took the opportunity to raid England when it presented itself, but this would be the last such raid.
Three main factors have played to stop the series of raids that have happened during the High Middle Age: