The USK was established alongside NATO as a subset of NATO in the late '50s. However, the Union had actually (as a union that had the nations monarchs under a common monarch) existed from the late 1500's to the reformation into the NATO subset version. the USK consisted of Denmark, Iceland, Sweden, Norway and Finland until the Soviet/Warsaw Union annexed Finland and the Bordering parts of Norway, ending Finnish membership. However NATO and the USK still work closely together despite NATO taking little to no action on the Communist annexation of Finland.
Traditional Union under Common Monarch (later part of 1500's-1950's)
The Scandinavian Union was established sometime in the late 1500's, but no one knows for sure when. The Union was originally just to keep Scandinavia tight-nit. Over the centuries different monarchs ruled over the separate nation's monarchs and Scandinavia until the 1950's.
Subdivision of NATO (1950's-)
The Union joined NATO as a subdivisio
n in the late '50s and continues under NATO. There is no longer a monarch but a representative who proposes ideas for the Union to NATO for approval.