From the 8th through 10th Century, Vikings raided and set up colonies in eastern Ireland. Later came the Norman invaders and the English, who subdued Ireland and suppressed its Gaelic language until the early 20th Century. With the arrival of the Roman Empire, Celtic civilization nearly disappeared. Most of Western Europe, except Ireland, was "Romanized."
These early people lived relatively undisturbed for centuries, cultivating a pastoral and agricultural economy, isolated from each other, absent of any real urban life. That made them particularly susceptible to the hardships that followed, notably the Great Potato Famine in the mid 19th Century. Most of the Catholic immigrants to the U.S. were impoverished people from rural Ireland who left after the catastrophic failure of the nation's staple food crop. The famine resulted in disease and starvation that killed at least one million people in Ireland and forced another million to flee the country. After the famine, emigration continued to function as an economic and social safety valve for Irish society, enabling people who could not earn a living in Ireland to seek their fortunes abroad. The early Irish used Celtic prefixes such as O' and Mac in surnames. Names beginning with O' (meaning grandfather or ancestor) can be traced back to the 11th Century. Most families whose surnames began with O' or Mac were Catholic.
