In the early 1800s, Irish farmers became almost entirely dependent on the growth of potatoes. Potatoes were the only crop that could sustain families on the tiny plots they worked. In the 1840s a fungus attacked the potato crops and caused a terrible famine. The famine devastated Ireland and changed it forever.
Before the famine, there were 8 million people alive on the island. Today there are only 5 million. At least one million died due to the famine and another million is thought to have immigrated to the US due to the famine. The famine also created greater resentment against the British, which led to Ireland's eventual independence.
The famine was caused by a fungus which made potatoes wither at an incredibly fast pace. This meant that crops that should have lasted them for 6 months were completely inedible. Crops failed for the harvests of 1845, 46 and 47!