1. The American Revolution (1775)

The United States had yet to even declare its independence from Great Britain when the Continental Army launched an invasion of the neighboring British colony of Canada in the summer of 1775. Setting out to seize Quebec City, the patriots hoped to gain a strategic location on the St. Lawrence River and recruit French-Canadians to join their rebellion. 

Colonel Benedict Arnold marched his forces north through the deep woods of Maine and in December 1775 met up on the outskirts of Quebec City with General Richard Montgomery’s men who had proceeded up Lake Champlain and seized Montreal. 

With the enlistments of many of his men expiring on New Year’s Day, Arnold was forced to launch a desperate attack on December 31, 1775, during the middle of a blizzard. The assault failed miserably, and Montgomery was among the dozens killed in the Battle of Quebec. The Continental Army eventually retreated from Canada, and in 1780 Arnold notoriously switched sides to join with the British.

2. War of 1812 (1812-1814)

After the United States declared war on Great Britain in June 1812, it launched a three-pronged invasion of Canada. Many American military and political leaders expected to encounter little resistance. “The acquisition of Canada,” wrote former President Thomas Jefferson, “will be a mere matter of marching.” 

The invaders were hardly greeted as liberators, however, and Canadians did not rise up to join them. William Hull’s invasion across the Detroit River in the war’s opening weeks ended in disaster with the American general surrendering his entire army and the town of Detroit without firing a shot. 

In October 1812, U.S. General Stephen Van Rensselaer’s forces crossed the Niagara River and were thrashed at the Battle of Queenston Heights. U.S. General Henry Dearborn’s plans to capture Montreal fizzled before he even crossed the border. American forces had more success launching smaller border raids throughout the War of 1812, as did their British counterparts. The Americans captured and torched the provincial capital of York (present-day Toronto) in 1813. Of course, the British did the same to Washington, D.C. the following year.

3. Patriot War (1838)

After the failure of a popular uprising in Upper Canada (present-day Ontario) in 1837, rebel leaders fled to the United States and found considerable support for their Republican aspirations. Canadian refugees and their American sympathizers formed secret organizations known as “Hunters’ Lodges” dedicated to freeing Canada from British rule. In November 1838, approximately 300 “Hunter Patriot” insurgents crossed the St. Lawrence River from New York state in an attempted invasion.

In the ensuing Battle of the Windmill, U.S. Army regulars and the U.S. Navy provided support to the British infantry and loyalist Canadian militiamen battling the invaders. More than 50 rebels were killed in the battle, and nearly a dozen more would be executed for treason. A few weeks later, 140 Hunter Patriots crossed the Detroit River and launched a second failed invasion attempt on the city of Windsor that forced the rebels to disband.

4. Pork & Beans War (1838-1839)

For decades after the American Revolution, a boundary dispute between Maine and New Brunswick simmered until Canadian lumberjacks were spotted felling trees in the disputed territory near the Aroostook River on December 29, 1838. Two days later, the rival timbermen drew arms, but the standoff ended when a black bear attacked three of the Canadians. Maine dispatched its land agent and volunteer militiamen to arrest the New Brunswickers, but the Canadians ended up seizing the land agent instead.

Both sides engaged in a series of arrests, and as tensions escalated, American President Martin Van Buren dispatched Brigadier General Winfield Scott to the disputed area, and Congress in the summer of 1839 authorized a 50,000-man force to be placed at Van Buren’s disposal in the event of an invasion. 

While American militiamen built forts along the border and used effigies of Queen Victoria for target practice, Scott worked with his Canadian counterpart to diffuse tensions. The “Aroostook War,” also called the “Pork & Beans War” for the popular diet of the local lumberjacks, ended with no combat deaths and the settlement of the Maine-Canadian border with the 1842 Webster-Ashburton Treaty.

5. Pig War (1859)

It may sound like a bunch of baloney, but the United States and Canada nearly went to war over a dead hog. On June 15, 1859, American farmer Lyman Cutlar killed a large black pig, owned by the Canadian Hudson’s Bay Company, that was eating the potatoes in his garden on San Juan Island, land off the coast of Washington claimed by both the United States and Canada. 

When British authorities threatened to arrest Cutlar and evict 17 of his fellow countrymen from the island, the U.S. Army dispatched 64 soldiers under Captain George Pickett—later of Gettysburg fame—to the island. British warships sailed to the island, but clear-headed British Rear Admiral Robert L. Baynes refused to attack and “involve two great nations in a war over a squabble about a pig.” 

For more than a decade, British and American troops peacefully occupied the island until an arbitration commission selected by Germany’s Kaiser Wilhelm I ruled in 1872 that the San Juan Islands were American territories.

6. Fenian Raids (1866-1871)

It may have been one of the most fantastical military operations ever concocted: In the wake of the Civil War, Irish-American veterans belonging to the Fenian Brotherhood plotted to invade the British colony of Canada and hold it “hostage” in return for the independence of Ireland. 

The United States government—still angered at British support of the Confederacy and the use of Canada as a safe haven by Confederate spies and raiders—turned a blind eye as thousands of battle-hardened Fenian troops amassed along the Canadian border in the spring of 1866. A plan to invade New Brunswick’s Campobello Island fizzled, but on June 1, 1866, more than 1,000 Fenians crossed the Niagara River from Buffalo and defeated a Canadian militia at the Battle of Ridgeway. 

Once the American government finally cut the Fenians’ supply lines and dispatched General Ulysses S. Grant to control his former troops, the fighters for Irish freedom were forced to return to the United States. 

Ironically, the Fenian Raids failed to bring independence to Ireland—but they did to Canada, which no longer trusted the British to defend its borders and became an autonomous entity in 1867. Subsequent Fenian invasions of Quebec in 1870 and Manitoba in 1871 ultimately proved more farcical than threatening.

7. Cypress Hills Massacre (1873)

The West was just as wild in Canada as it was in the United States during the early 1870s, and rogue American fur and whiskey traders regularly breached the Canadian border and clashed with native tribes. On June 1, 1873, a group of wolf hunters and whiskey traders from Fort Benton, Montana, joined with Canadian traders to attack a camp of Assiniboine that they believed had stolen their horses.

The battle in the highlands of present-day Saskatchewan resulted in the deaths of at least 20 Assiniboine and one French-Canadian wolf hunter. The Cypress Hills Massacre demonstrated the need for the newly established Canadian confederation to police its lawless western territories, and it hastened the dispatch of the newly formed North-West Mounted Police, known as the “Mounties,” to establish order.