Irish petit bourgeois republican revolutionaries, who were active from the second half of the 19th century to the early 20th century. The Fenians were members of the Irish Republican Brotherhood (IRB), a group of secret organizations, which was formed in 1858, with centers in the USA and Ireland. In the 1860’s and 1870’s, IRB organizations spread throughout Ireland and Great Britain and became established among Irish immigrants in the USA, Canada, Australia, and other countries.

The Fenians sought to bring about the creation of an independent Irish republic by means of a clandestinely prepared armed rebellion. Their movement reflected the Irish people’s disaffection with British colonial rule—a disaffection made more acute by a British campaign, particularly during the second half of the 19th century, to evict Irish tenants from the land. Yet, because of their conspiratorial activities and their leaders’ tendency to give secondary consideration to the social and economic demands of the peasantry and proletariat, the Fenians failed to win wide support among the Irish people. In March 1867, when they provoked uncoordinated uprisings in various counties of Ireland, the Fenians were quickly defeated.

The First International declared its support of the Fenians, although it criticized their tendency toward conspiratorial activities. From 1867 to 1870 the First International took part in efforts to have the death sentences that had been imposed on participants in the Fenian movement commuted, and it appealed for amnesty for all Fenian prisoners.

The Fenians turned increasingly toward terrorism during the 1870’s and 1880’s. In the USA during the mid-1860’s, the IRB was dominated by a faction that advocated armed attacks on Canada as a way of bringing about war between Great Britain and the USA; such a conflict, they believed, would create favorable conditions for a struggle in Ireland itself. Between the late 19th century and the early 20th century, some Fenians left the IRB to join other organizations fighting for the independence of Ireland. Members of the Fenian movement took part in the Easter Rising in 1916.