Early Scandinavian Dublin
In the year 795 Vikings (probably of Norwegian origin) raided islands off the coast of Ireland for the first time. This was the beginning of a new phase of Irish history, which saw many native communities – particularly ecclesiastical ones – relocate themselves on the continent, or further afield in places like Iceland and the Faroe Islands, to escape the pagan marauders. For about two decades the invaders confined their activities to coastal settlements; raiding parties were generally small and there is no evidence that any of them wintered in Ireland during this early phase of "hit-and-run" activity. Typically the Vikings would arrive at a settlement without warning, plunder what goods and people they could – the people were usually sold as slaves, though notable personages were often held for ransom – before retreating to their Scandinavian or British bases. This period lasted from 795 until 813, after which there occurred a hiatus of eight years.
It is now thought that these early raids were launched directly from southwest Norway, and that during the period of calm (814–820) the Norwegian Vikings were occupied in northern Britain, laying the foundations of a new kingdom referred to in Irish sources as Laithlind (later Lochlainn). Laithlind was once thought to be in Norway but it is now identified with Viking settlements in the British Isles, especially those in Scotland and the Isle of Man.
Denmark
From the 8th to the 10th century the wider Scandinavian region was the source of Vikings. They colonised, raided, and traded in all parts of Europe. The Danish Vikings were most active in the eastern and southern British Isles and Western Europe. They conquered and settled parts of England (known as the Danelaw) under King Sweyn Forkbeard in 1013, and France where Danes and Norwegians founded Normandy with Rollo as head of state. More Anglo-Saxon pence of this period have been found in Denmark than in England.
Denmark was largely consolidated by the late 8th century and its rulers are consistently referred to in Frankish sources as kings ("reges"). Under the reign of Gudfred in 804 the Danish kingdom may have included all the lands of Jutland, Scania and the Danish islands, excluding Bornholm.
The extant Danish monarchy traces its roots back to Gorm the Old, who established his reign in the early 10th century. As attested by the Jelling stones, the Danes were Christianised around 965 by Harald Bluetooth, the son of Gorm. It is believed that Denmark became Christian for political reasons so as not to get invaded by the rising Christian power in Europe, the Holy Roman Empire, which was an important trading area for the Danes. In that case, Harald built six fortresses around Denmark called Trelleborg and built a further Danevirke. In the early 11th century, Canute the Great won and united Denmark, England, and Norway for almost 30 years with a Scandinavian army.