Much of the Catholic growth in nineteenth century America was due to Irish numbers and Irish leadership. Father John Lancaster Spalding, a future Bishop of Peoria and the driving force behind the founding of The Catholic University of America, had this to say in his 1880 book The Religious Mission of the Irish People:
The general truth is that the Irish Catholics are the most important element in the Church of this country… Were it not for Ireland, Catholicism would today be feeble and non-progressive in England, America, and Australia… The Irish have made the work… possible and effective … have given… a vigor and cohesiveness which enables it to assimilate the most heterogeneous elements and without which it is not at all certain that the vast majority of Catholic emigrating hither from other lands would not have been lost to the Church… No other people… could have done for the Catholic faith in the United States what the Irish people have done… No other people had received the same providential training for this work; of no other people had God required such proofs of love.