Colonel John O'Neill, the former U.S. cavalry officer who had led the first Fenian raid into Canada in 1866, launched what would prove to be the final Fenian attack against Canada. In the months leading up to the attack, he had managed to accumulate 15,000 rifles and 3 million rounds of ammunition in farmhouses along the Quebec-Vermont border.
O'Neill's force advanced into Canada on 25 May 1870, and Canadian militia units were quickly mobilized to meet the Fenian incursion. The Canadian force was comprised of companies from the 60th Mississquoi Volunteer Battalion, the Victoria Rifles of Montreal, the 1st Prince of Wales Rifles, the 5th Royals, the 6th Hochelaga Light Infantry, the Montreal Troop of Cavalry, and a detachment of the Montreal Garrison Artillery.
The Fenians were routed at the battles of Eccles Hill and Pigeon Hill, and the disheartened remnants of the "Irish Republican Army" straggled back to Vermont. As a result, the Fenian movement lost the majority of its support, and, within a year, it would collapse entirely.