Fenianism, according to O'Mahony,(Founder of the Fenian Brotherhood in the United States 1858) is symbolised by two principles: firstly, that Ireland has a natural right to independence, and secondly, that that right could be won only by an armed revolution.

The Fenian Brotherhood trace their origins back to 1798 and the United Irishmen, and are the previous revolution movement to the IRB

The Irish Republican Brotherhood (IRB) was a secret oath-bound fraternal organisation dedicated to the establishment of an "independent democratic republic" in Ireland during the second half of the 19th century and the start of the 20th century. Its counterpart in the United States of America was organized by John O'Mahony and became known as the Fenian Brotherhood (later Clan na Gael).The members of both wings of the movement are often referred to as "Fenians". The IRB played an important role in the history of Ireland, as the chief advocate of republicanism during the campaign for Ireland's independence from the United Kingdom, successor to movements such as the United Irishmen of the 1790s and the Young Irelanders of the 1840s.