Those Irish Americans are the offspring of some 6-8 million immigrants since around 1750. The biggest surges of emigration occurred in 1815-55. Initially this was driven by economic decline following the end of the Napoleonic wars. At first these were mostly Protestant dissenters. More Catholic emigration began in the 1830s and the Famine created a flood of emigrants; a significantly poorer group than before.

Ireland was not a dynamic economy and if a young man or woman wanted to prosper and marry but was not in line to inherit a farm or business there was not much opportunity during economic downturns.

Why did they choose the USA? It offered opportunity, considerable freedom and was English speaking. Poorer people migrated to the industrial cities of Britain. There typical emigrant to the US had poor prospects at home but could afford passage.

Once a strong Irish community was established various "pull" factors were added such as having friends or family already in place or positive stories about the US taken from letters home.

By the late nineteenth century, a culture of emigration had been established which lasts today. Although emigration is seen as a problem, it is understood as a normal response to bad times.