He was widely considered the primary leader of the modernizing element in the Catholic Church in the United States during the Progressive Era, which brought him into open conflict over minority language rights and theology with both his suffragen Bishop Otto Zardetti and eventually with Pope Leo XIII, whose Apostolic letter Testem benevolentiae nostrae condemned Archbishop Ireland's ideas as the heresy of Americanism.

One year later Joseph Crétin, first bishop of Saint Paul, sent Ireland to the preparatory seminary of Meximieux in France.

The influence of his personality made Archbishop Ireland a commanding figure in many important movements, especially those for total abstinence, for colonization in the Northwest, and modern education.

This organization bought land in rural areas to the west and south and helped resettle Irish Catholics from the urban slums.

From 1876 to 1881 Ireland organized and directed the most successful rural colonization program ever sponsored by the Catholic Church in the U.S.[1] Working with the western railroads and with the Minnesota state government, he brought more than 4,000 Catholic families from the slums of eastern urban areas and settled them on more than 400,000 acres (1,600 km2) of farmland in rural Minnesota.

[1] His partner in Ireland was John Sweetman, a wealthy brewer who helped set up the Irish-American Colonisation Company there.

They arrived at the wrong time of the year and had to be assisted by local Freemasons, an organisation that the Catholic Church condemns on many points.

In the public debate that followed, the immigrants, being Connaught Irish monoglot speakers, could not voice their opinions of Bishop Ireland's criticism of their acceptance of the Masons' support during a harsh winter.

[23] Charlotte Grace O'Brien, philanthropist and activist for the protection of female emigrants, found that often the illiterate young women were being tricked into prostitution through spurious offers of employment.

Ireland agreed to raise the matter at the May 1883 meeting of the Irish Catholic Association which endorsed the plan and voted to establish an information bureau at Castle Garden.

Ireland influenced American society by actively demanding the immediate adoption of the English language by German-Americans and other recent immigrants.

Zardetti later played a major role, as an official of the Roman Curia, in pushing for the Apostolic letter Testem Benevolentiae, which was signed by Pope Leo XIII on 22 January 1899.

Yzermans has commented, "In this arena he might well have had seen his greatest impact on American Catholicism in the first half of the twentieth century in the United States.

[31] Forced into an impasse, Toth went on to lead thousands of Ruthenian Catholics out of the Roman Communion and into what would eventually become the Orthodox Church in America.

[34] In 1885 Ireland was appointed to a committee, along with, Bishop John Lancaster Spalding, Cardinal James Gibbons and then bishop John Joseph Keane dedicated to developing and establishing The Catholic University of America in Washington, D.C.[34] Ireland retained an active interest in the university for the rest of his life.

The Saint Paul Seminary was established with the help of Methodist James J. Hill, whose wife, Mary Mehegan, was a devout Catholic.

[37] At the same time, on Christmas Day 1903 he also commissioned the construction of the almost equally large Church of Saint Mary, for the Immaculate Conception parish in the neighboring city of Minneapolis.