Potatoes are native to the Americas and were a staple of the Inca diet. Originally, Europeans did not want to eat them. Potatoes were actually brought to a European royal court soon after the discovery of the New World and the cooks, not knowing how to cook them, threw away the potatoes and only cooked the eyes, which are poisonous. Everyone got sick and potatoes were banned in that country for awhile, I think it was Britain.
Potatoes eventually really took root in Ireland where they were perfectly suited to the rocky soil which was not so easy to farm on generally. With the high amount of calories potatoes could produce per acre and the fact that it's an incredibly nutritious food, potatoes soon became a staple of the Irish diet. Because they only had one strain of potatoes, the potatoes in Ireland were susceptible to some type of potato-destroying bug that caused the Irish potato famine. The Irish were so reliant on potatoes that without them lots of people starved and many others came to America and other countries to escape. Potatoes today are much more resistant to disease. Potatoes spread and are widely eaten now in Europe. There are lots of potatoes eaten in the British isles, Germany and Russia and Eastern Europe.
In America, potato cultivation is found more so than anywhere in Idaho but also in surrounding states like Oregon and Washington and in Maine. Potatoes are grown to some extent all over. In Idaho they even have potato ice cream ... I've never had it but it sounds kind of weird.
North Korea a few years ago launched a "potato revolution." That country has had many famines and has had a hard time growing enough food to feed its population. Potatoes there had traditionally been known as a poor people's food, but they also have rocky soil suited to potato growing. Kim Jong Il has hoped to reverse the country's inability to feed itself by encouraging more farming and consumption of potatoes.