What did cause the war between Marleyans and Eldians?


I'm finding answers for my book. It's about a war between Marleyans and
Eldians but it did not tell in the manga what caused the war so I was looking
for some help.




**Major manga spoilers below!**

> After obtaining power of Titans, eldians started massive ethnic cleansing,
> and marlians became one of the victims of this act, naturally inflicting
> massive hatred towards eldians.

[Source](http://attackontitan.wikia.com/wiki/Marley)

