Re WWII: In most of Europe and even the Balkans, much of what you said is true.
However, WWII Croatia WAS a unique case. The only WWII deathcamps in Europe not run by Nazi Germany were in Croatia. Look up Jasenovac or Croatian Ustashe just as overviews. Croatia was a particularly brutal and sadistic state during WWII, with behavior that even appalled Germans.
Cicero: beware of Serbian propagandists and their claims. The Jasenovac Research Institute for example engaged in a gross lie in which they published the names of 700,000 purported victims of the Ustashi in Jasenovac. It turned out that over 90% of the names were names of those who perished elsewhere, hundreds of thousands of which were on the Axis side during the war!
At last count, I've found 110 relatives on the list and I can assure you that not one of them was a victim of Ustashi terror. For instance, two of my greatgrandparents were killed in an Allied air raid in October 1944, but both their names appear on the list of "victims of Ustashi terror" on the Jasenovac Research Institute site.
Always, always take Serbian claims with a two handfuls of salt.