The Fenians were an Irish nationalist secret society that had relocated from Ireland to the United States. Between 1866 and 1871, they launched several small armed attacks, all suppressed by government forces. The incidents occurred in Sarnia, Windsor, Niagara, Quebec, Manitoba, and Amherstburg, Ontario. According to the Canadian Encyclopedia, some members tried to seize Canadian territory by force to exchange it with Britain for Ireland’s independence. 

These raids profoundly impacted the Canadian militia, exposing weaknesses in its leadership, organization, and training, prompting significant improvements. The attacks intensified fears regarding American military and economic strength, leading to more excellent backing for the Canadian Confederation and the formation of the Dominion of Canada in 1867. The confrontation with the Fenian was Canada’s first modern battle, entirely fought and led by Canadian soldiers and officers.