That doesn't make sense. Potatoes have never been a particularly good cash crop. What they are marvelous at is subsistence agriculture. In their own lands the

That doesn't make sense. Potatoes have never been a particularly good cash crop. What they are marvelous at is subsistence agriculture. In their own lands the feudal overlords had eliminated both feudal overlordship and subsistence agriculture trough some incredibly unpopular land reforms - the highland clearances of Scotland and the enclosure acts of England. Basically they told the peasants the land is now property of the feudal overlord and that they should get a job. For various political reasons nobody wanted to do the same in Ireland.