I've been watching this excellent series about irish history This episode deals with the potato famine which, it says, lasted for 5 years. Most people who have a grip of history know how awful it was and that is re-iterated in the film. What it doesn't say is why it ended. Was it simply a case that so many people had died or emigrated the food supply was now enough? Did they find a way to combat the blight, stop it from spreading, even early pesticides? Or did the potatoes slowly start to resist blight through natural selection? Or something else?