Denmark comprises, more or less, OTL Denmark.
In 1940, Denmark is invaded by the Third Reich and annexed for 46 years.
The Reich policies preserved Danish culture and language but demanded German language as obligatory subject in schools. Denmark was managed as a Reich "Land".
When the civil war started in 1979 soon several independentist movements arose in Denmark, but none of them could manage a majority in the Land's government.
In 1986 the Reich was dissolved. Soon a coalition of independentist movements declared Danish independence and a constituent assambly was convoked.
In January 1st, 1987, Denmark was declared an independent republic under parliamentary model.