[15][16][17] Divisions between Irish Roman Catholics and Irish Protestants played a major role in the history of Ireland from the 16th century to the 20th century, especially during the Home Rule Crisis and the Troubles.

While religion broadly marks the delineation of these divisions, the contentions were primarily political and they were also related to access to power.

In the Irish Rebellion of 1798, Catholics and Presbyterians, who were not part of the established Church of Ireland, found common cause.

Emigration exponentially increased due to the Great Famine which lasted from 1845 to 1852.

By the 20th century, Irish Catholics were well established in the United States and today they are fully-integrated into mainstream American society with two Irish Catholic Presidents, John F. Kennedy and Joe Biden, having been elected.