Let me tell you a story, which I heard from my cousin 15 years ago. The tale begins with the ‘Schleswig–Holstein Question’, one of the knottiest of the many problems in the tangled web of 19th-century European politics. As British foreign secretary Lord Palmerston is reputed to have said, “The Schleswig–Holstein Question is so complicated, only three men in Europe have ever understood it. One was Prince Albert, who is dead. The second was a German professor, who became mad. I am the third, and I have forgotten all about it.”
In essence, the duchies of Schleswig and Holstein were the possessions of the Danish Crown, with a mixed German and Danish population. In Schleswig, the northern duchy, there was a Danish majority, while in Holstein the Germans predominated. Prussia,…