In 1845 Ireland’s potato crop failed. Though crop failures in Europe were widespread at the time, the blight in Ireland was particularly hard hitting because of the reliance on a single crop, potatoes, as the primary source of sustenance. The Great Famine that resulted lasted until 1848. The effect was a drastic decline in the Irish population—due both to deaths and to emigration. Between 700,000 and 1 million people died in Ireland during the Great Famine. And between 1846 and 1854 alone, 1.75 million left the country in search of a better life elsewhere. Three-quarters of those were headed to the United States.

In the years after the Great Famine, experts determined that the blight of the late 1840s was caused by a fungus that was probably introduced to Ireland by a ship from North America, where there had been crop failures in the early 1840s. Sad irony that the very conduit that had likely borne the blight from North America to Ireland also carried immigrating Irish back to North American shores.