[MIL.com] In the years following the American Civil War, Canada was still very much a possession of the British Empire. As such, it had a number of official fortifications and other important areas along its border with the United States.One of those was Fort Erie, directly across the Niagara from the American city of Buffalo, New York. In June 1866, some 850 men crossed the Niagara from Buffalo, intent on capturing the fort.
They were Irishmen, and they were going to conquer Canada to free their home country.
Irish immigrants flowed into the United States in droves following the Acts of Union that saw British domination of Ireland since the early 1800s. The Great Irish Famine of the late 1840s also saw a huge emigration of Irish people to the United States.
By 1860, there were more than 1.6 million people of Irish descent who called themselves American ‐ and upwards of 175,000 of them were about to serve in the Union Army.
The Irish made-up 40 percent of foreign-born enlistments in the Civil War, and were 17 percent of the overall Union force. When these battle-hardened veterans returned home after the war, many of them were headed to New York, Pennsylvania, New Jersey, and New England. It was there that Irish National leaders were waiting to use the veterans' new talent for combat.