Irish myth differs from many other cultures because there is no creation element. Where some cultures have the manifestation of deity or elemental beings becoming the physical world in which we live, in the oldest Irish stories, Ireland just is.
The origin stories of Irish myth are collectively known as Lebor Gabála Eireann, which is translated as the Book of Invasions, or the Book of the taking of Ireland.
The Tuatha Dé Dannan are said to have come out of their four cities and journeyed around on their route back to Ireland collecting every occult or hidden druidic knowledge.
What made them more resilient than other peoples was their knowledge of healing. Knowledge that predominantly rested with one man.