principle cause of the famine was mono-culture.

some large (say 80%) of potatoes were one type. The fungus spread because it had a big target. It was also susceptible to light - it grew faster in the light. Farmers covered the potatoes to slow (or prevent as they thought) the blight.

History repeats itself, it has to nobody is listening.

viz I give you Microsoft Windows and Cavendish bananas

both are subject to viruses (or fungii in the case of bananas) which spread easily due to mono-culture. Bananas are a special case as they effectively only propagate vegitatively, with human intervention. They don't generate seeds (or so rarely as to be effectively sterile). Making all bananas clones, how easy is that as a target?