Why did Irish emigrate to the US?

During the Great Famine in Ireland (1845 to 1852), the absentee landlords (mostly English) who owned the land in Ireland, saw the failure of crops and therefore their tenants inability to pay rent as a good opportunity to get rid of a lot of relatively unproductive tenants.

These tenants often starved, but some made it into the towns and cites. Work and accomodation were very short but America was openly inviting new immigrants with promises of jobs in the cities and land in the West for the more intrepid.

Timing is everything.