By the turn of the century , according to some reckonings, 70 percent of Irish manufactured exports were by US-owned firms…
This was, of course, encouraged by tax breaks and a form of industrial policy. But part of this process was a shift away from English investment:
Between 1960 and 1970 British-owned companies represented 22 percent of new industrial enterprises in Ireland. But by 1980 they accounted for less than 2 percent. Significantly, the proportion of exports to Britain from Ireland halved between 1956 and 1981.
In other words, Ireland found a more complementary economic partner, namely the United States. The Irish economic miracle is in part the American economic miracle.
That is from the often interesting Luck & the Irish: A Brief History of Change from 1970, by R.F. Foster. Here is a previous MR post on the Irish economic miracle.