The settlement of Iceland () is generally believed to have begun in the second half of the ninth century, when Norse settlers migrated across the North Atlantic. The reasons for the migration are uncertain: later in the Middle Ages Icelanders themselves tended to cite civil strife brought about by the ambitions of the Norwegian king Harald I of Norway, but modern historians focus on deeper factors, such as a shortage of arable land in Scandinavia. Unlike Britain and Ireland, Iceland was unsettled land and could be claimed without conflict with existing inhabitants.