Complex sentence: Catalans Americans refuse to be identified as Hispanic, mainly because they have Catalan as their mother tongue instead of Castilian and that's why the modern definition of Hispanic has historically excluded those peoples from Spain who did not have Spanish as their mother tongue.
Split into simpler sentences: Catalans Americans refuse to be identified as Hispanic, mainly because they have Catalan as their mother tongue instead of Castilian. This is why the modern definition of Hispanic has historically excluded those peoples from Spain who did not have Spanish as their mother tongue.