IN 1866, one of the strangest armies in American history marched off to war.
Made up of Irish-born Civil War veterans from both northern and southern states, this unlikely brigade was united with a single goal in mind – to break the British stranglehold over their native Ireland.
To make good on their objective, the leaders of this bizarre movement, known as the Fenian Brotherhood, planned to unleash a legion of Irish expats on Great Britain’s Canadian colonies. The transplanted patriots hoped to use the captured territories as a bargaining chip in negotiations with London for the independence of their ancestral homeland.
On paper, the Fenian scheme looked feasible enough. The Brotherhood could draw from up to 17,000 combat-hardened, Irish-born Civil War veterans. Surplus arms and equipment were stockpiled at secret depots around the country. Financial backing from scores of Irish Americans was pouring in and a provisional government was ready and waiting in New York. The Fenians believed they could even count on tacit support from the U.S. government, which was still irked by Britain’s sympathy for the southern rebellion. To the Brotherhood, the campaign to seize Canada seemed entirely plausible. Unfortunately for them, things just didn’t work out that way.
The Back Story
The Fenian Brotherhood was established on the 1850s as an American offshoot of the United Irishmen, an 18th Century movement that launched an anti-British insurgency in the old country. By 1860, prominent Fenians recognized that the coming war between the states was a golden opportunity for their members to learn how to fight together as an army: something they hoped to do later against the British Empire. Accordingly, Kingpins like John O’Mahony and William Roberts used the occasion to raise regiments of fellow expats in New York, Chicago and Philadelphia, while their compatriots in the southern states, like Father John Bannon, helped organize groups of Irish volunteers below the Mason Dixon. 
While northern and southern Irish troops did occasionally do battle with one another during the Civil War, often the opposing regiments would arrange informal parlays or “soldiers truces” whenever they could. Generals on both sides frequently turned a blind eye to the gatherings, believing them to be largely harmless reunions among kinsmen. In reality, the summits enabled the Fenians to draw up their plans for a post war campaign against Britain’s New World colonies. 
With the fighting finally over in 1865, the Fenians decided that the time to act was at hand. The Brotherhood’s leadership met in the latter half of the year to fine-tun their plot against Canada and put out the call to members to assemble. One of their marshalling points was Buffalo, New York, a border town on the American side of the Niagara River. Another was Maine. Brotherhood officials even met with U.S. president Andrew Johnson who indicated that Washington would likely not interfere in the event of hostilities and might even formally recognize the Fenian cause if it succeeded.  By the spring of 1866, thousands of vets from both Union and Confederacy had been rallied, arms and ammunition were distributed, officers were appointed and final plans of attack were shared.
In April, the Fenians made their first foray onto Canadian soil. A detachment of 1,000 in Maine seized Campobello Island, which was part of the British colony of New Brunswick, Canada.
An even larger operation took place a few weeks later on the Great Lakes.
On June 1, a battalion of 1,300 Fenians under the command of Col. John O’Neill, formerly an officer of the 5th Indiana Cavalry, crossed the mouth of the Niagara at Buffalo, NY into Canada.  Members of the invasion force, which came from New York, Ohio, Tennessee, Louisiana and Kentucky, descended onto the border town of Fort Erie and secured it with minimal resistance.  The strategy was to establish a foothold in the Niagara Region and then march onto Toronto, Montreal and even Quebec City.
Surprised and unprepared, the Canadian authorities quickly slapped together a force of nearly 1,000 militia, along with a handful of regulars, and rushed the whole column off to meet the Fenians. Recognizing that their men would soon be facing an army of seasoned vets, Canadian commanders armed their force with a brand new consignment of Spencer repeating rifles. The brass hoped the added firepower would make up for their side’s lack of experience. Unfortunately, few of the novice defenders had ever handled the weapons before, let alone fired them. They were used to training with old muzzle-loading muskets. 
Learning that British and Canadian troops were en route, O’Neill left a small force to hold Fort Erie and set off to intercept the enemy. The two armies met outside the village of Ridgeway, Ontario on the morning of June 2.
The 90 minute engagement that followed saw the Canadians initially push the Fenians back. But when a handful of Irish mounted scouts appeared, the redcoats mistakenly took the small formation for the vanguard of a much larger cavalry force. The defenders quickly formed squares but in the confusion left themselves open to a Fenian bayonet charge.  The British and Canadians were driven from the field, leaving seven dead and more than 60 wounded. For their part, the Fenians lost six men while 10 were injured.
The Invasion Fizzles
Despite the victory at Ridgway, O’Neill realized his foothold in Canada was growing more tenuous by the hour. Scores of British and Canadian reinforcements were converging on the Niagara from the west and north. Worse, the American government, which had previously maintained a policy of benign indifference to the Fenian cause, was now wary of provoking a war with Britain. Following the initial landings at Fort Erie, the gunboat USS Michigan had taken up a station off Buffalo and was turning back any Fenian reinforcements that tried to cross into Canada. Meanwhile military authorities in New York State under the command of no less than generals Ulysses Grant and George Meade arrived in western New York with orders to disarm and arrest the Fenians. Realizing his forces were alone in Canada and cut off from fresh troops and supplies, O’Neill beat a hasty retreat to the stronghold of Fort Erie, but not before clashing again with a force of fresh Canadian militia. Despite capturing more than 50 of the volunteers at Fort Erie, the Fenian commander recognized that the tide had turned and ordered a general withdrawal. The Fenians retreated right into the waiting arms of U.S. authorities.
The End of the Dream
Within days of their failed gambit on the Great Lakes, the Fenians would send more insurgents into New Brunswick, but they too were pushed back by Canadian forces and again intercepted by the U.S. military.
Fenians were now on Washington’s public enemies list. It became ever more difficult for them to gather, while the police and army were quick to pounce on their stockpiles of arms and equipment.
Other smaller forays were mounted against Quebec and border points on the Canadian prairies in 1870 and 1871 respectively, but these were quickly dispersed by authorities on both sides of the border.
With their numbers dwindling and their rank-and-file finally settling down into civilian life in greater numbers, the Brotherhood’s schemes became even more desperate and outlandish.
In 1881, the group financed a 30-foot long submarine dubbed The Fenian Ram, ostensibly to be used against British shipping. Unable to find a crew to operate it, the sub was mothballed in 1883, only to be pulled from storage in 1916 for use as a public attraction at Irish Republican fundraisers in the United States. 
Ironically, while the Fenians sought to break the British stranglehold over Ireland, the only country to gain independence as a result of its 1866 raids was Canada. The attacks, which were largely repelled by local militia, generated a new surge of patriotic fervor in Canada that would be a factor in the colonies’ amicable independence from Great Britain in 1867.
Ireland would finally achieve independence from Great Britain in 1922 following its own war of independence between 1919 and 1921.