Many authors have covered this complex subject. Excerpts from some of their writings are provided here. For interested readers, a bibliography is provided. 

From ancient times, Irish myth conjured lands to the west across the Atlantic and circumstantial evidence  suggests that Brendan the Navigator (St. Brendan ) confirmed those legends in a documented 7th century voyage in a hide skinned boat to the "Land of Promise and Saints".

The later voyage of Columbus in 1492 is no less free of Irish involvement; some would say, indeed contend,  that he depended sorely on the Irish sailor from Galway (one Ayers or Eris)who accompanied him.

From the earliest precolonial period, the Irish have streamed to America imprinting a distinct and indelible mark on American culture. Some were men and women of standing before they arrived; others dug, scraped, swept, hauled and tended. In their adopted motherland they built canals and railroads, fought in all her wars; swept back her frontiers, organized her working class and formed and ascended her cultural steppes to become renowned in the arts, in politics, in all the professions and in every facet of American life.

It was not a painless journey:

"Like the Indians, they have suffered loss of their ancestral land; like the blacks, they have endured bondage; like the Jews, they have tasted religious persecution; like the Asians, they have been scorned because they looked and acted "different"; like the Italians and the Slavs, they have been despised as "poor and ignorant"; like the Hispanics, they have been denounced as violent and disruptive."  Griffin, William D., The Book of Irish Americans, Times Books (New York, 1990) 

There is much to be learned from this remarkable story.