Ireland was certainly producing plenty of other crops than potatoes but when I said they were lacking biodiversity I was specifically referencing the potato monoculture. The poor were overwhelmingly reliant on the potato and it was wiped out by a blight that could have been largely avoided with a broader diversity of potatoes being grown. Similarly there are plenty of banana varieties around the world, but the only one sold in grocery stores near me is being wiped out by blight. Imagine if something similar happened to corn or wheat. An aggressive blight on a main cultivar would be pretty devastating, even if there are still lots of heirloom varieties being grown in small quantities around the world.