The question should be about Ireland in 1840s and not 1940s.
Between 1845 and 1852, over a million people in Ireland starved to death due to the failure of the potato crop in Ireland. Potatoes were the staple diet in Ireland. However, during this period, potato crops were affected by a disease known as the potato blight. As a result, the production of potatoes fell drastically leaving people little to eat. This resulted in mass starvation and deaths in Ireland. This episode is called the Irish potato famine.