What Progressive reform was the most
important for the Americans of this era?

Important changes introduced at the national levels included the imposition of an income tax with the Sixteenth Amendment, automatic election of Senators with the Seventeenth Amendment, Prohibition with the Eighteenth Amendment, election laws to stop graft and bribery, and women's suffrage.

general allotment act (dawes act) february 8, 1887

amendment to the dawes act, february 28, 1891

commission to the five civilized tribes (dawes commission), march 3, 1893