Stumbled across a piece on the Irish potato famine. Its effects varied in different parts of the island, hitting particularly hard in the south and west, areas which were much more dependent on the potato and had fewer other resources.
While many died and many left, others moved within Ireland, moving north and east to Belfast and Dublin. For the former, the writer observed that where Belfast used to be almost entirely Protestant, because of the internal migrants being Catholic it became a more divided place. (I'm not sure whether Catholics also moved to other places in Ulster.) Those divisions led to the "Troubles" of the last pat of the 20th century, which led to the importance of the peace agreement in British and Irish politics, which led to the Brexit conundrum Incidentally, it reminds me of the anecdote about the horse who get hung up jumping a fence.