What sparked irish immigration to the united states in the mid-1840s?

Irish Immigrants came to the United States in the early part of the 19th century because there was the Potato Famine in Ireland. This caused starvation and forced the Irish to immigrant to another place. This place was the US. Additionally, the Northeastern part of the US including New York City offered employment as dock or factory workers. People from Ireland have made up a substantial part of the US population from European nations.

The Irish immigration back then was mainly because of the potato famine issue.

Both countries had to aprove annexation.