The ostensible reason for the Ottomans invading Hungary
That's why I said catholic on catholic. Non-catholic on Catholic could and did happen for any reason under the sun (Albigensian crusade, 4th crusade, any other crusade).
Think of it like a matrix with culture on one axis and religious on another axis. The closer two lords were, the less likely they would fight an all-out war without a serious reason. Farther apart = more likely to kill lots of people for not a lot of reason.
Religious wars in particular were the biggest 'land grabs,' e.g. the Iberian conquest and reconquista and of course the Holy land.
