/u/platypuskeeper (which is me, but a bot will complain if I don't link it) wrote an answer to a similar question a few days ago.

The Viking Age is not like the Stone, Bronze or Iron Ages, as in being reasonably well-defined from archaeological evidence. In that system, the Viking Age is the end of the Iron Age, followed by the Middle Ages. (so the Scandinavian Middle Ages begin later than in continental Europe)

As said in my earlier post, there are a number of things that define the Viking Age, none of which give any sharply-defined dates. The conventional dates for the end of the Viking Age are in the mid-11th century, e.g. 1050 for an even number or 1066 for the Battle of Stamford Bridge. In any case the end of the Viking Age is certainly by definition connected to the establishment of Christianity and the social, economic and cultural changes connected with it.

One might imagine from that, that Vikings converted and decided that raiding and such was un-Christian and therefore stopped. That's not really the case though. The conversion of Scandinavia was a drawn out process, almost as long as the Viking Age itself if you count from it establishing itself among the nobility in Denmark in the early-mid 10th century, until the last known pagan incidents in the early 12th century in Sweden. And if you count it from the first Christian influences on Scandinavian society, then it's as long as (and almost concurrent with) the entire Viking Age.

I would not say Christianity caused the 'decline' of the Viking Age though because I don't see a sense in which it really declined. Certainly the amount of raiding in western Europe declined after the rapid rise of it in the 9th century. So that would actually have been on the decline well before Christianity was fully established. A few sporadic raids in the British isles and Ireland occurred until at least 1103, and Scandinavians continued to travel the eastern route down to Byzantium for at least a century after that. The frequent warring between Scandinavian kings and nobles, in a fashion not unsimilar to the events in the Sagas, continued for several centuries as well. One thing that mrks the eginning of the Viking Age is also the founding and growth of market towns, like Hedeby, Birka and Kaupang. None of those specific towns survived the Viking Age (Hedeby being destroyed last, in 1050) but others founded during it (e.g Nidaros/Trondheim) exist to this day. The Viking Age saw the establishment of the first undisputed national kings of Denmark, Norway and Sweden, the beginning of coinage, the first written histories from Scandinavia (even if written down later), the building of churches, many things that would only continue and increase in following centuries.

So the Viking Age marked the end of some things - notably paganism, it also saw the beginning of many things that were to continue. When it comes to Viking raiders, it saw both the rise and decline of them.