The hatred between the Serbians and Croatians is racial. The hatred between Muslims and both groups is religious bigotry.
My brother in law escaped from Communist Yugoslavia, and hates Serbs with a purple passion. The Croatians supported the Muslims destroying Serbia, because they hated the Serbians more.
In WW2, the Serbs supported the Allies. The Croatians supported Nazis. Early in the war they invited the forces of Serbians to a meeting to discuss how to best enter the war, it was a trap and they slaughtered many Serbians.
Long story short, that area is full of hate, centuries old and it has nothing to do with the color of the skin. It is Catholic versus Orthodox versus Muslim. Communist versus Liberty versus Islamic law.
Welcome to the Balkans America, it sounds just like here in 2020.
You will find this interesting and troubling:
Serb
WWII: The Savage Revolution
https://www.youtube.com/watch?v=hHuqWxFaQ50&list=PLzxzphEuxjOtf4fNvHbcAHODNQ9oiOSXM&index=2
These were/are real people. They survived, many did not.
Hour long vid.
There were two resistance movements--the Chetniks were mostly Serbs and Montenegrins. The Partisans, led by Tito, drew from all the ethnic groups. At first they seem to have been mostly Serbs (Tito himself was a Croat) but a lot of Croats also joined the Partisans. To make a blanket statement that the Croatians supported the Nazis is misleading when many Croats died fighting the Axis (Germans and Italians).
Nikola Tesla was an ethnic Serb from Croatia who lived most of his life in the US and wanted nothing to do with the Serb/Croat animosity. He had nothing to do with Bosnia.