Originally Posted by Aviatrix

Denmark did not join Schengen at the very beginning, and the "irrelevant" fact that it is part of Scandinavia is in fact the very reason it wasn't able to join Schengen from Day 1!

Long before Schengen there was the Nordic Common Travel Area (established in the 1950s) - which included a non-EU member state, Norway. It was Norway's membership in the Nordic Common Travel Area which delayed Denmark's entry into Schengen - the Nordic countries did not implement the Schengen Agreement until 2001.