The Northern Isles, which consist of the two island groups of Shetland and Orkney, have been inhabited since prehistoric times but were formally annexed by the Norwegian king Harald Hårfagre in around 875 after he subdued the Vikings who used the islands as a base from which to raid Norway and Scotland.

Christian II had invaded Sweden in an attempt to preserve the Kalmar Union that joined the Scandinavian countries of Denmark, Sweden and Norway under a single monarch.