Fenianism was a political movement in the mid-nineteenth century in favour of an independent Ireland. Its name comes from the mythological Fianna army of Fionn MacCumhail. The Fenians originated among the Irish immigrants in the United States in the 1840s. The beginnings of the Fenian movement followed the collapse Young Ireland movement and the movement for the repeal of the Act of Union.
The Fenians were given shape by the establishment of the Irish Republican Brotherhood in 1858 in Dublin by James Stephens. This organisation was committed to the establishment of a democratic Irish Republic and was highly secretive. The Fenians attempted armed uprisings in February and March of 1867, but both attempts failed. Government informers, a well-prepared British army and unsuitable weather conditions ensured the Fenians' lack of success.
The treatment of Fenian prisoners influenced public opinion in favour of Irish independence. Three men were hanged after an attempt to rescue two Fenian prisoners in Manchester, England, in 1867. They were William O'Meara Allen, Michael Larkin and William O'Brien, commonly called the 'Manchester Martyrs'. Their execution caused a groundswell of public support for the Fenian movement in Ireland. The movement also had a strong influence on later Irish nationalism, both political and cultural. For example, W.B. Yeates was deeply influenced in his youth by his friendship with the old Fenian, John O'Leary.