As explained by historian Stephen Davies, after defeating James II in 1690, protestants subjected Irish Catholics to harsh restrictions on land ownership and leasing. Most of Ireland’s people were thus forced to farm plots of land that were inefficiently small and on which they had no incentives to make long-term improvements. As a consequence, Irish agricultural productivity stagnated, and, in turn, the high-yield, highly nutritious, and labor-intensive potato became the dominant crop. In combination with interventions that obstructed Catholics from engaging in modern commercial activities – interventions that kept large numbers of Irish practicing subsistence agriculture well into the 19th century – this over-dependence on the potato spelled doom when in 1845 that crop became infected with the fungus Phytophthora infestans.
To make matters worse, Britain’s high-tariff “corn laws” discouraged the importation of grains that would have lessened the starvation. Indeed, one of Britain’s most famous moves toward laissez faire – the 1846 repeal of the corn laws – was partly a response to the famine in Ireland.
Had laissez faire in fact reigned in Ireland in the mid-19th century, the potato famine almost certainly would never had happened.