The nation had been on a diet of potatoes because of the rarity of meat, which had become a once a month treat.
Potatoes were only introduced to Ireland in the 1600s but became a dominant food by the latter 1800s. The vegetable took to the Gaelic soil for several reasons:
This very reliance, however, also caused problems. For one, there was no trade in food. Everyone had the same crop, removing any incentive to grow something different or farm more efficiently. Also, as history proved, one single disease can ruin a whole nation.
Part of the shock of the event was the fact that it was a 13th-century-style famine happening in the 19th century. Apart from the one and a half million people who died, at least one million others left for England or America.
It would have been quite easy to repeal the Corn Laws forbidding the import of grain to Ireland. English employers could have broken with tradition and paid acceptable wages. Typically, Catholic employees were poorly paid because British bosses felt increased pay meant increased family size, thus further reducing the ratio of Protestants to Catholics.
Britain did eventually administering some emergency shipments of food but lacked the administrative know-how to carry out their own policies. Poor houses constructed by the state in the 1830s had been so poorly managed since their conception that they were no help. Also, the social stigmatism attached to welfare programs was so high, even the most downtrodden wouldn't always accept aid.
Even when emergency shipments of grain did arrive from America, rural Ireland didn't have the network of shops to distribute the goods, and, generally, no one in those regions knew how to grind corn or make bread.
One other major result was the elevation of the agrarian dimension of Ireland. Naturally, because of the suffering, initial thoughts of Ireland were always about the farmers, who now had an intensified hatred of Great Britain.
Of course, all of the immigration helped to transport Irish nationalism to the English-speaking world, especially the United States.