Heaney spent a year as a guest lecturer in UC Berkeley in 1970-'71 and realised there that his daily life in Northern Ireland had become dominated by the Troubles to an extent that was harming his development as a writer.

After that, he moved south of the border and spent 4 productive years as a full-time writer in Wicklow (a rural county south of Dublin and quite far from the conflict). He called his time in Wicklow a "retreat" in the religious sense of the word, emphasizing how it was about getting away from the world. Then, from 1976, he started taking academic jobs outside of Northern Ireland, first in Dublin and then in America.

Since long before he left Northern Ireland, he'd have been considered a prominent Nationalist by both sides, so the move south should have seemed more like opting out of the conflict than taking a side in it.