There was a potato famine and thousands of people were starving to death
Catholicism.
The Irish immigrated because of the Irish Potato Famine in 1845
Most of the immigration was caused by the potato famine, but some were caused when their king had switched to a England church because of his marriage. That caused England to be in control of Ireland which left them weak. Another when the black plague had spread to them from England and the Irish were mad at them cause now, England had made most of their troubles.
Well the irish immigration came in three waves. The first and second "wave" came after 1717. Then the last (3rd) wave was in the mid 19th century (1840s). But the majority of the Irish Immigration was during the 1800s. From about 1841-1850 the U.S recorded 780,719 Irish immigrants. The number is a rough calculation but its probably close.
Most of the Irish immigrants who came to the United States to escape the Potato Famine settled in and around Boston and New York. The main reason was they didn't come to the country with very much money, and lacked the resources to move further inland.
Northeast
Caused violence in New York, when new Irish immigrants were drafted into the Union army. In the South, one of the most respected Confederate Generals was the Irish-born pharmacist, Pat Cleburne.
Ireland
women & children
Northern and mid-Atlantic port cities.New York, Boston, Philadelphia, and Chicago--but all over the US, actually.
Ireland and Germany
The most famous massive Irish immigration to the US was around the 1840s due to the major potato famine in Ireland.