...why should Slavonia go to Bosnia?
That is ludicrous.
There were no tensions between Croats and Serbs prior to the 19th century.
The Croatian and Serbian nobility cooperated and intermarried constantly, what you are stating makes no sense.
A Serbian noble served two terms as ban of Croatia and a two Croatian nobles served as Despots of Serbia.
There was no inert hostility, otherwise Croatian knights would not have answered Serbia's call for aid and fought at Kosovo.
Also, your map extends Serbia to far to the West.