In the 1840s it was because of famine. In other times there were various reasons, but all amounting to people going in search of a better life. They were getting away from things like poverty, unemployment, political issues and violence, amongst other things.
a famine
I am not sure but i think it was mostly Ireland. however there were immigrants from Poland, Germany, Bulgaria and England
immigrants from Ireland come form Ireland.
The people of Delaware came from Sweden, Holand, and England.
Eventually some went back but mostly they stayed where they moved to and spread.
There was about 500,000 Irish immigrants in 1900
Ireland and Germany
ireland
They arrived in between 1845 to 1860 the immigrants where from Ireland and Germany
Immigration from Ireland was mostly a result of a potato famine. The reason it's called an Irish Potato is because the Irish depended greatly on the potato and when a blight was destroying the potato crops one million died and others came here.
The southern part. Northern Ireland was mostly Catholic.
The 19th century saw immigration explode in the United States. From 1820 to 1890, an estimated 28,293,000 people immigrated to the U.S. Many of these immigrants came from Germany, Ireland, Italy, Austria-Hungary, Russia, and England.