Religious persecution, extreme poverty, crop failures, and overcrowding forced nearly 3.5 million Irish people to abandon their homeland and seek prosperity in the United States between 1820 and 1880. Ireland’s poor peasant class suffered the greatest hardships. In 1660, less than one million people lived in Ireland. By 1840, the population had jumped to eight million. This had a large effect on landless Irish, who toiled desperately on patches of ground rented from absentee land owners. To accommodate the increase in people, land holdings were divided into smaller parcels. Most farmers weren’t able to produce enough food from these two- or three-acre plots to feed their families. Then disaster struck. The potato famine of 1845 pushed families who depended on milk and potatoes to starvation. As a result, many abandoned their homeland. Irish immigration peaked during the 1840s, when two million people arrived on America’s shores. Most settled in the cities where they landed: mainly New York City, Boston, Philadelphia, and Baltimore. Soon, the Irish were establishing churches and building communities. Also, Irish laborers became the mainstay of construction crews who built the canal and railroad systems of this country.