The harsh penal laws of two centuries ago prescribing transportation and long terms of penal servitude were a compelling agency in driving the Irish to America.  Illiberal laws against religious nonconformists, especially against the Catholics, closed the doors of political advancement in their faces, submitted them to humiliating discriminations, and drove many from the island.  Finally, the selfish Navigation Laws forbade both exportation of cattle to England and the sending of foodstuffs to the colonies, dealing thereby a heavy blow to Irish agriculture.  These restrictions were followed by other inhibitions until almost every industry or business in which the Irish engaged was unduly limited and controlled.  It should, however, not be forgotten that these restrictions bore with equal weight upon the Ulster settlers from Scotland and England, who managed somehow to endure them successfully.

Absentee landlordism was oppressive both to the cotter’s body and to his soul, for it not only bound him to perpetual poverty but kindled within him a deep sense of injustice.  The historian, Justin McCarthy, says that the Irishman “regarded the right to have a bit of land, his share, exactly as other people regard the right to live.”  So political and economic conditions combined to feed the discontent of a people peculiarly sensitive to wrongs and swift in their resentments.

But the most potent cause of the great Irish influx into America was famine in Ireland.  The economist may well ascribe Irish failure to the potato.  Here was a crop so easy of culture and of such nourishing qualities that it led to overpopulation and all its attendant ills.  The failure of this crop was indeed an “overwhelming disaster,” for, according to Justin McCarthy, the Irish peasant with his wife and his family lived on the potato, and whole generations grew up, lived, married, and passed away without ever having tasted meat.  When the cold and damp summer of 1845 brought the potato rot, the little, overpopulated island was facing dire want.  But when the next two years brought a plant disease that destroyed the entire crop, then famine and fever claimed one quarter of the eight million inhabitants.  The pitiful details of this national disaster touched American hearts.  Fleets of relief ships were sent across from America, and many a shipload of Irish peasants was brought back.  In 1845 over 44,821 came; 1847 saw this number rise to 105,536 and in the next year to 112,934.  Rebellion following the famine swelled the number of immigrants until Ireland was left a land of old people with a fast shrinking population.