Answer:
In simple words, Poverty and drought, most especially the potato famine in Ireland, were the drive forces forcing immigrants to migrate to the USA. Immigrants had little prospects in Europe so moved to the USA in pursuit of more paid jobs.
About four million European settlers immigrated to the united states over the time 1840 to 1860, mostly from Ireland as well as Germany.The industrialization propelled the growth of the manufacturing system , especially in the northeastern, whereby industrial ization, shipping, and agriculture fuelled economic development and generated a need the need for more more jobs.