Sweden. They also settled in the Faroe Islands, Ireland, Iceland, peripheral Scotland (Caithness, the Hebrides and the Northern Isles), Greenland, and Canada. Their North Germanic language, Old Norse, became the precursor to present-day Scandinavian languages. By 801, a strong central authority appears to have been established in Jutland, and the Danes were beginning to look beyond their own territory for land, trade, and plunder. In Norway, mountainous terrain and fjords formed strong natural boundaries. Communities remained independent of each other, unlike the situation in lowland Denmark. By 800, some 30 small kingdoms existed in Norway. The sea was the easiest way of communication between the Norwegian kingdoms and the outside world. In the eighth century, Scandinavians began to build ships of war and send them on raiding expeditions which started the Viking Age. The North Sea rovers were traders, colonisers, explorers, and plunderers who were notorious in England, Scotland, Ireland, Wales and other places in Europe for being brutal. Probable causes of Norse expansion Many theories are posited for the cause of the Viking invasions; the will to explore likely played a major role. At the time, England, Wales, and Ireland were vulnerable to attack, being divided into many different warring kingdoms in a state of internal disarray, while the Franks were well defended. Overpopulation, especially near the Scandes, was a possible reason, although some disagree with this theory. Technological advances like the use of iron and a shortage of women due to selective female infanticide also likely had an impact. Tensions caused by Frankish expansion to the south of Scandinavia, and their subsequent attacks upon the Viking peoples, may have also played a role in Viking pillaging. Harald I of Norway ("Harald Fairhair") had united Norway around this time and displaced many peoples. As a result, these people sought for new bases to launch counter-raids against Harald. Debate among scholars is ongoing as to why the Scandinavians began to expand from the eighth through 11th centuries. Various factors have been highlighted: demographic, economic, ideological, political, technological, and environmental. Demographic model This model suggests that Scandinavia experienced a population boom just before the Viking Age began. The agricultural capacity of the land was not enough to keep up with the increasing population. As a result, many Scandinavians found themselves with no property and no status. To remedy this, these landless men took to piracy to obtain material wealth. The population