it's believed to have been an old island arc, about 30 million years ago
based on shape it looks like it was a chunk of island arc that subducted the wrong way for a while before the situaiton stabilised in current aleutian arc
Ambiguous, there was an arbitration between Slovenia and Croatia, but it came out that the Slovenian side bribed the judges, so Croatia pulled out before the ruling was passed.
The judges did end up ruling in Slovenia's favor, and Slovenia tried finding support in Europe for enforcing it, but they failed.