The Irish Potato Famine, which lasted from 1845 to 1850, resulted in a great exodus of Irish refugees fleeing to Britain, Australia, and North America, one of the most dramatic waves of Irish migration in history.

From 1740 onwards, the population of Ireland began to soar. For the next eighty years, the largely agricultural economy of Ireland enjoyed a period of prosperity due to increased production and high British grain demands. However, by the 1830s, the once-fertile soil had grown depleted from heavy overproduction, and agricultural productivity fell off.

Britain began to turn elsewhere to meet its agricultural needs and Ireland grew increasingly unable to meet even its own needs. Irish landowners reacted in their own interests, expelling tenant farmers, or forcing them to subsist on minuscule plots of land. Life became increasingly harsh as the potato crop began to fail regularly and thousands of people began to emigrate in desperate hope of survival.

The mid-1840s marked the onset of catastrophe for the Irish potato crop. A partial failure of the vital staple crop in 1845 was followed by a complete failure the following year, which was in turn followed by an especially cruel winter. In 1848, the crop failed once again. Starvation and disease became common as many farmers were driven penniless from their homes.

From 1845 to 1851, Ireland lost almost a quarter of its population. Of these, half emigrated to Britain, North America, and Australia. The other half perished. The Potato Famine brought unprecedented elements to Irish migration because most of the migrants were unfortunate refugees, rather than voluntary emigrants. They were more likely to be diseased and destitute and as the source areas for migrants grew to include all of Ireland, the majority came from more remote areas which had been previously underrepresented.

Consequently, they were far less likely to be integrated into the commercial economy and were, on the whole, less skilled. Most were virtually penniless and were often perceived to be lower-class and less hard-working, but nothing could be further from the truth. Time would prove their critics very wrong. The vast majority of Famine refugees chose the United States as their destination. This Irish intrusion proved to be a potent force for change in the New World that became the backbone of the American way of life.