When nationalism combines with soccer in the stadiums and streets of Europe, it tends to not end well.

For decades, images of drunken fans adorned with nationalist symbols and flags fighting one another – or the police – have dogged the UEFA European Championship, a competition between teams from across the continent that takes place every four years.

So it is perhaps understandable that German authorities were fearing the worst in advance of hosting the current championship, which began on June 14 and concludes on July 14 with a final between Spain and England.

After all,…