https://en.m.wikipedia.org/wiki/Great_Famine_(Ireland)

A fungus and land mismanagement, among other things lightly outlined in the article above.

A dependence on the single crop of potato was a result of British land owners limiting crops to a single one that grew well, followed by a fungal infection from the conditions. Potatoes aren’t native to Ireland, so there will be diseases it encounters there that it wouldn’t in SA.

Single crop growing is not a good idea for anyone. The dust bowl is bound to happen again as long as we continue to till up land for one plant in one spot instead of interspecies growing.