Actually, you could say that religion motivated Oliver Cromwell and the English, when they murdered thousands of Irish women and children at such places as Drogheda. But these massacres were also the result of theories of warfare of that time, and they were also a matter of English vs. Irish, conquerors and conquered, resistence and oppression.
OTOH, the modern Irish revolutionary movement, beginning in the late nineteenth century and continuing through most of the twentieth, was NOT motivated by Catholicism to any great degree. The two factions are conveniently known as Protestants and Catholics, but they are primarily native Irish versus English/Scottish conquerors, with religion to help keep the two groups separate over time. But also there were rules of the conqueror to keep the two groups separate, with the English and Scots firmly in the controlling positions and the Irish not permitted to own a horse, learn to read, or attend a university for a couple of centuries.
The modern IRA is primarily Marxist in orientation, not Catholic. It has never had much if any support from the Irish bishops or the official Church. It would be foolish to say that religion had nothing to do with the hatreds in Ireland, but religion was rarely a primary motivating force for the violence there, except to some degree on the Orange side.
If not for religion, would the bloodshed in Ireland not have occurred? Very doubtful. The primary motivators were conquest, colonialism, repression, and resentment for being oppressed by outsiders.
Did religion cause the split in South Africa? In that case, we turn to race for an explanation, because it marks the most prominent difference. But there is seldom a single cause for such problems. In South Africa there were three or four groups: Zulus, Xhosa, Dutch, English. The Dutch and the English hated each other as much as the Zulus and English. It was not simply a matter of black vs. white, although that came to be the accepted wisdom.