In the Fenian Invasion of Canada, John O'Neill leads 850 Fenian raiders across the Niagara River at Buffalo, New York/Fort Erie, Ontario, as part of an effort to free Ireland from the United Kingdom. Canadian militia and British regulars repulse the invaders over the next three days, at a cost of nine dead and 38 wounded to the 19 dead and about 17 wounded Fenians.
The Fenian raids were carried out by the Fenian Brotherhood, an Irish Republican organization based in the United States, on British Army forts, customs posts and other targets in Canada, in 1866, and again from 1870 to 1871. A number of separate incursions by the Fenian Brotherhood into Canada were undertaken to bring pressure on Great Britain to withdraw from Ireland, although none of these raids achieved their aims.
In Canada, the incursions divided its Catholic Irish-Canadian population, many of whom were torn between loyalty to their new home and sympathy for the aims of the Fenians. The Protestant Irish were generally loyal to the British and fought with the pro Union Orange Order against the Fenians.
While authorities in the United States arrested the men and confiscated the arms of the Fenian Brotherhood, there was speculation that some in the United States government had ignored the preparations undertaken by the Fenians because of anger over actions that could have been construed as British assistance to the Confederate States of America during the American Civil War.