Fenians.

This is coolbert:

Consider this a new one on me. USA and Canada in disagreement and combat action as a result. The Fenian Raids. Not necessarily the USA and Canada in disagreement however.

Thanks to the tip from Lemuel.

"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 the United Kingdom to withdraw from Ireland, although none of these raids achieved their aims."

INVASION CANADA USA!

Ethnic Irish residing in the USA. Natural born and naturalized citizens and legal aliens. Men opposed to British rule in Ireland. Attempting to exert pressure on the British government. A FREE AND INDEPENDENT IRELAND THE GOAL!

Men too with considerable combat experience, well armed, led by officers also with considerable combat experience. ALL [?] veterans of the American Civil War.

Several "invasions" border-crossing from USA to Canada resulting in relatively minor casualties. A point however was made.

INVASION NEITHER APPROVED OR SANCTIONED BY THE AMERICAN GOVERNMENT. FENIANS FREE-LANCERS.

Canadians responding appropriately:

"The greatest impact of the Fenian raids was in developing a sense of Canadian nationalism and leading the provinces into a Confederation. This was . . . important factor in creating the modern nation-state of Canada."

coolbert.