As long ago as over 12,000 years, as far back in time as the end of the last Ice Age, the ancestors of the Vikings were wandering across what is now referred to as Scandinavia: namely Norway, Sweden and Denmark. Their way of life as hunter-gatherers and fishermen was to last for thousands of years, despite climate changes, tribal movements and a great upheaval of people across Europe over this period of time.
Geography
Although the people of Scandinavia shared a common ancestry and elements of culture, such as art and house- and boat-building, the huge geographical differences between many of the areas meant that communities made their livings in very different ways, and had different problems with which to contend.
The Danish isles contained flat and fertile agricultural land, and while the Gulf Stream warmed the Norwegian coastline, a spine of mountains running north-south separated Norway from Sweden with few accessible passes. The northern realms were geographically very separate entities, and even by the end of the Viking Age could not be said to be fully controlled by their supposed kings.
Language
Phonological changes occurred in Scandinavian language between the years 600 and 800, making it less like their southern Germanic neighbours or neighbouring Finns, Lapps or Slavs, and cementing the Norse identity and common culture of Norway, Sweden and Denmark.
Jarls
Provinces were ruled by independent Jarls, and some of the first raiders identified themselves as men of Hordaland (those who killed the king’s reeve at Dorchester in 789) or Vestfold (those who attacked Aquitaine in 840) rather than Norwegian.
Travel and Battle
The standard society grouping centred on the family. It was a much broader concept than today, taking in multiple generations and all their offspring who would work on the family farm or business for the benefit and honour of all. They would generally all live as well as work together, in longhouses.
Despite the geographical isolation of parts of Scandinavia and the strength of the family unit, by the time of the Viking era, kings were looking to consolidate their grip on larger regions and groups of men began to look further afield for land and riches. There is little evidence to suggest that population pressure or lack of land was responsible for forcing Scandinavian men to leave their homeland, but perhaps powerful and threatening neighbours were making it an attractive proposition. There is also the possibility that the three-tier caste system of Norse society made it difficult for Jarls or freemen who were not wealthy to obtain wives and that this was another driving force, with young men venturing abroad for female slaves who would act as concubines.
Scandinavian society was pagan in religion, worshipping a pantheon of gods and practicing sacrificial rituals, including human. Their major deities were gods of strife, Odin and Thor, and dying in battle was necessary for a warrior to ascend to join Odin in Valhalla. With no shortage of inter-regional warfare Norsemen never lacked for skill or aggression in battle, and, when combined with superb ship-building skills, sea-borne raiding could be seen as a natural evolution.