In Ireland, the Great Famine was a period of mass starvation, disease and emigration between 1845 and 1852. It is sometimes referred to, mostly outside Ireland, as the Irish Potato Famine because one-third of the population was then solely reliant on this cheap crop (which originated in the New World) for a number of historical reasons. During the famine approximately a million people died and a million more emigrated from Ireland, causing the island's population to fall by between 20% and 25%. The proximate cause of famine was a potato disease commonly known as potato blight.
Due to the effects of the Potato Famine, many people from Ireland immigrated to the North American Union. They came over a decade after the emancipation of North American slaves and the abolishment of slavery in the rest of the British Empire. Consequently, the immigrants were given jobs that involved hard and dangerous labour such as mining, while the Negroes were given safer and more "respectable" civil service positions. This caused friction between the two ethnic groups.