The Balkans is a region of southeastern Europe, named for the mountain range. Historically, it has been a conflicted region of multiple ethnicities and religions.
Balkans in In High Places
In one alternate, the Balkans were conquered by Muslims shortly after the Great Black Deaths decimated 80% of Europe's population. Annette Klein privately noted that the Muslims did a much more thorough job of keeping the Balkans under control than any conqueror of the same region in the home timeline.
Balkans in In the Presence of Mine Enemies
The Balkans remained under the rule of the Greater German Reich after it emerged victorious from World War II. The lone exception was Croatia, which remained an independent ally of the Reich due to its homegrown fascist government, which was heavily influenced by the Nazi model.
The region was nonetheless restive, particularly the state of Serbia.
Balkans in Southern Victory
Otto von Bismarck is reputed to have said: "Some damn fool thing in the Balkans will start a major war." In 1914, that is precisely what happened, as Archduke Franz Ferdinand of Austria-Hungary and his wife Duchess Sophie were assassinated by Serbian nationalists, triggering the various alliance systems in place in Europe and North America, and starting the Great War.
Balkans in Worldwar
Many Balkan countries such as Serbia were known for the fierce guerrilla resistance they put up against would-be occupiers. The region remained under German control after the Race-German War of 1965 even though other parts of Europe broke free from Nazi domination.