Where you get that he was Croatian in the first place?
"Nikola Tesla was born to Serbian parents in the village of Smiljan, Austrian Empire near the town of Gospić, in the territory of modern-day Croatia. His baptismal certificate reports that he was born on 28 June (N.S. 10 July) 1856 to father Milutin Tesla, a priest in the Serbian Orthodox Church.[12] His mother was Đuka Tesla, née Mandić, whose father was also a Serbian Orthodox priest."
"Nikola Tesla was born to Serbian parents in the village of Smiljan, Austrian Empire near the town of Gospić, in the territory of modern-day Croatia. His baptismal certificate reports that he was born on 28 June (N.S. 10 July) 1856 to father Milutin Tesla, a priest in the Serbian Orthodox Church.[12] His mother was Đuka Tesla, née Mandić, whose father was also a Serbian Orthodox priest."
It doesn't get any more Serbian.