While we fought our 'Great Civil War' (Abe Lincoln) , the second military conflict over Schleswig-Holstein succession question was being fought in Europe. It pitted Prussia and Austria against Denmark, who long controlled the two duchies. The disputes was against the Danish king who died without an acceptable heir. Acceptable to the German Confederation. And then there was the passing of a joint Danish/Schleswig constitution, which didn’t go over very well, either. German won, and in Denmark ceded control of both duchies.