The primary cause of the Irish Potato Famine in the 19th century was the failure of the potato crop due to a devastating blight caused by the fungus Phytophthora infestans. Potatoes were a staple food for the Irish population, and their destruction in the mid-1840s led to widespread hunger and malnutrition. The implications were catastrophic; about one million people died, and another million emigrated, significantly impacting Ireland's demographic and cultural landscape. The famine exacerbated pre-existing social and economic inequalities, exposing the failures of British governance in Ireland. It prompted discussions on land ownership, agricultural practices, and the role of government in crisis management.