The Irish had 6 waves of invasions BEFORE the Christians. Each group worshipped different God's. It's recounted in the Myth of Tuan Mac Carril. The book that contains the myths of Pre-Christian Ireland is called The Book of Invasions.
The last group of pre-Christian invaders - the Milsians fought the Tuatha Da Danaan gods for the Island. There was intense animosity between them after the 2nd battle of Moy Turra.
When Christianity came to Ireland the Irish couldn't wait to convert because the old gods disliked them.