At the beginning of the 19th century the dominant industry of Ireland was agriculture. Large areas of this land was under the control of landowners living in England. Much of this land was rented to small farmers who, because of a lack of capital, farmed with antiquated implements and used backward methods.
The average wage for farm labourers in Ireland was eight pence a day. This was only a fifth of what could be obtained in the United States and those without land began to seriously consider emigrating to the New World.
In 1816 around 6,000 Irish people sailed for America. Within two years this figure had doubled. Early arrivals were recruited to build canals. In 1818 over 3,000 Irish labourers were employed on the Erie Canal. By 1826 around 5,000 were working on four separate canal projects. One journalist commented: "There are several kinds of power working at the fabric of the republic - water-power, steam-power and Irish-power. The last works hardest of all."
In October 1845 a serious blight began among the Irish potatoes, ruining about three-quarters of the country's crop. This was a disaster as over four million people in Ireland depended on the potato as their chief food. The blight returned in 1846 and over the next year an estimated 350,000 people died of starvation and an outbreak of typhus that ravaged a weaken population. Despite good potato crops over the next four years, people continued to die and in 1851 the Census Commissioners estimated that nearly a million people had died during the Irish Famine. The British administration and absentee landlords were blamed for this catastrophe by the Irish people.
The Irish Famine stimulated a desire to emigrate. The figures for this period show a dramatic increase in Irish people arriving in the United States: 92,484 in 1846, 196,224 in 1847, 173,744 in 1848, 204,771 in 1849, and 206,041 in 1850. By the end of 1854 nearly two million people - about a quarter of the population - had emigrated to the United States in ten years.
A census carried out in 1850 revealed that there were 961,719 people in the United States that had been born in Ireland. At this time they mainly lived in New York, Pennsylvania, Massachusetts, Illinois, Ohio and New Jersey. The Irish Emigrant Society tried to persuade immigrants to move to the interior but the vast majority were poverty-stricken and had no money for transport or to buy land. They therefore tended to settle close to the port where they disembarked.
Thousands of Irish labourers worked on building the railroads in the United States. Some were able to save enough money to buy land and establish themselves as farmers along the routes they had helped to develop. This was especially true of Illinois and by 1860 there were 87,000 Irish people living in this state.
Other Irish immigrants became coalminers in Pennsylvania. Working conditions in the mines were appalling with no safety requirements, no official inspections and no proper ventilation. When workers were victimized for trade union activity, they formed a secret society called the Molly Maguires. Named after an anti-landlord organization in Ireland, the group attempted to intimidate mine-owners and their supporters. The group was not broken-up until 1875 when James McParland, a Pinkerton detective and Irish imigrant, infiltrated the organization and his evidence resulted in the execution of twenty of its members.
The Irish tended to support the Democratic Party rather than the Republican Party. They had little sympathy for slaves as they feared that if they were given their freedom they would move north and threaten the jobs being done by Irish immigrants. One leading Irish-American politician, John Mitchel, wrote in his newspaper, The Citizen in 1856: "He would be a bad Irishman who voted for principles which jeopardized the present freedom of a nation of white men, for the vague forlorn hope of elevating blacks to a level for which it is at least problematical whether God and nature ever intended them."
However, on the outbreak of the Civil War general an estimated 170,000 men born in Ireland joined the Union Army, whereas only 40,000 were in the Confederate Army. One Irish immigrant, Thomas Meagher, became a highly successful general in the war.
After the Civil War some cities in the United States such as New York, Chicago and Boston, over a quarter of the population had been born in Ireland. It was now possible Irish voters were able to get their candidates elected to power. Irish mayors such as Richard Croker of New York and James Curley in Boston were accused of corruption by investigative journalists such as Ray Stannard Baker and Lincoln Steffens.
However, as the historian Carl Wittke has pointed out: "Reformers have often overlooked the fact that the same political boss who bought votes, stuffed ballot boxes, and brazenly perpetuated naturalization frauds was also the warmhearted leader who got the immigrant his pushcart license, "fixed" arrests for petty violations of the law with the police and the judge, and sent the poor their Christmas turkeys and coal in winter, paid their rent when the landlord threatened eviction, and sent flowers to their funerals."
Several Irish settlers became successful businessmen. Michael Cudahy started a highly profitable meat-packing business in Milwaukee, John Downey made a fortune in real estate as well as being governor of California (1861-62) and William Grace ran a steamship company before becoming mayor of New York City (1880-88). Second-generation businessmen included James Phelan (banking) and mayor of San Francisco (1896-1902), Thomas Ryan (financier), Franklin Gowen (railroads and coalmines), John Francis Fitzgerald (investment banker) and mayor of Boston (1906-08, 1910-14) and Patrick Joseph Kennedy (wine and spirit importater).
In 1890 there were large numbers of Irish born immigrants in the states of New York (483,000), Massachusetts (260,000), Illinois (124,000) and Minnesota (28,000). There were also significant communities in New York City (190,000), Chicago (70,000), Baltimore (13,000) and the textile town of Lawrence (8,000).
During the period 1820 and 1920 over 4,400,000 people emigrated from Ireland to the United States. Only Germany (5,500,000) and Italy (4,190,000) came anywhere near these figures. In 1840 Ireland had been the most densely populated country in Europe. By the 20th century this situation had been completely reversed.
An investigation carried out in 1978 revealled that since 1820 over 4,723,000 people emigrated to the United States from Ireland. This amounted to 9.7 per cent of the total foreign immigration during this period.