Wikipedia says in the article Folk Music of Ireland:

"From the end of the second world war until the late fifties folk music was held in low regard. Comhaltas Ceoltóirí Éireann (an Irish traditional music association) and the popularity of the Fleadh Cheoil (music festival) helped lead the revival of the music. The English Folk music scene also encouraged and gave self confidence to many Irish musicians. Following the success of The Clancy Brothers in the USA in 1959, Irish folk music became fashionable again."