On December 29, 1837, a group of Canadian militiamen crossed the Niagara in silence and boarded the Caroline. The fight was short but sharp, and those Americans who refused to surrender were "dealt with according to the usages of war".  One American was killed, the rest were taken prisoner and the Caroline itself was set ablaze and sent hurtling over the falls.

The destruction of the Caroline caused much anger in the United States, and many believed that the time had come to destroy the meddling British and expel them from North America. Indeed, it did much to attract American "hunters" to the cause of the Canadian rebels, and could be partially responsible for the Niagara invasion of 1838.

The United States government was also furious at this breach of American neutrality. They demanded monetary compensation from the British, who refused. The affair threatened to boil over when a Canadian who boasted of being one of the militiamen who captured the Caroline was arrested by American authorities and tried for murder. War was prevented only by his aquittal.

Peaceful relations between the U.S. and Great Britain were restored in 1842 with the signing of the Webster-Ashburton Treaty, in which Britain expressed regret for destruction of the Caroline and apologized. 

The Aroostook War, 1839

See also:

• Webster-Ashburton Treaty

When the United States government began issuing land grants to settlers in the Aroostook river valley, a part of the disputed zone, the British protested. The King of Holland arbitrated the dispute, setting the boundary in the middle of the disputed area. The Americans complied for a while, but went back on the agreement in 1832.

This caused much anger on the Canadian side of the border. In 1838, Canadian lumberjacks entered the Aroostook valley to cut timber, and in February of 1839, they seized an American land agent who had been sent to eject them. Tempers began to rise as both Maine and New Brunswick called out their militias. Congress, at the request of Maine, authorized a force of 50,000 troops and appropriated $10 million to fund it.

At this time, President Van Buren intervened and directed General Winfield Scott to arrange a meeting between the two parties. Both sides agreed to hand the dispute to a boundary commission, who settled the matter in the Webster-Ashburton Treaty of 1842. The United States was given 7,000 square miles of the valley, and the British 5,000. The treaty granted enough land to the U.S. to placate their more warlike factions, and ensured the British a direct military link to Montreal.

The Oregon Dispute
Crisis sprung from the American claim to the entire Pacific coast as far north as Russian American, encompasing all of modern-day British Columbia and Washington state west of the Rocky Mountains.

The British had contended that they had sole ownership of the area in question because of George Vancouver's survey of the coast in 1792 and Simon Fraser's trading post, the first built west of the Rockies. The Hudson's Bay Company also had several forts built in the area.

The Americans countered these claims by arguing that Robert Gray's and Lewis and Clark's expeditions into the area gave American sovereignty over them. They also claimed that an American fur trading post, Fort Astoria, which was based in the Oregon Territory, gave them rights over the land, even though the fort had been sold to the North-West Company in 1813.

The two sides adopted a very militant attitude, with American president Polk adopting the slogan "Fifty-four forty or fight!" and the British constructing four redoubts around the strategic city of Kingston, in Upper Canada. In the end, however, the British and Americans agreed to a treaty setting the boundary to the 49°N that was in place east of the Rockies.

The Pig War, 1859
With its roots in the Oregon Crisis of 1846, the Pig War was not really a war at all, but a standoff which very nearly erupted into open battle. In the end, however, the only casualty was a champion breeder pig.

As a result of the Oregon Treaty, the boundary between the United States and British Columbia was set at the 49th Parallel. However, it was unclear where the boundary existed in the Juan de Fuca straights, and directly in the middle of these straights sat the San Juan islands. Consequently, both the U.S. and Great Britain unofficially claimed ownership to the islands.

In 1854, an American customs collector arrived on San Juan island and attempted to collect taxes on a Hudson's Bay Company sheep farm located on the island. The farmers refused, and a warrant was put out for the arrest of the Americans, who promptly left. A year later, a U.S. sheriff and ten armed vigilantes stole 35 sheep belonging to the Hudson's Bay Company as compensation for back taxes. The H.B.C. claimed appealed to Governor Douglas of British Columbia, who then brought the matter up with Governor Stevens of Washington Territory. Although nothing came of these events, they did much to arouse ill-will between the British and American parties in the area.

Several attempts by government agents to fix the boundary failed. Finally, in 1859, a pig belonging to the H.B.C. escaped from its pen and wound up rooting for potatoes in the garden of Lyman A. Cutlar, an American farmer. Cutlar shot the pig, but realizing that it had belonged to the H.B.C., he offered to compensate them for it. The H.B.C. informed Cutlar that the pig had been a champion breeder and demanded $100 for it. Cutlar refused, and in consequence was told that he was trespassing on British territory and would be arrested if he did not pay for the pig. 

At this time, Brigadier-General William S. Harney of the U.S. Military Department of Oregon arrived on the scene. Foul tempered and rabidly anglophobic, Harney ordered Company D, 9th U.S. Infantry, under the command of Captain Pickett (later of Pickett's Charge fame) to establish a military post on the island, called "American Camp". A meeting between Pickett and Captain Geoffery Hornby of the Royal Navy produced no diplomatic results, save for Pickett's declaration that he would not allow the British to occupy the island unless directly ordered to do so from Brigadier-General Harney.

Harney was pleased with Pickett's audacity and despatched reinforcements to the island. This time, the British responded in force, sending five warships (totalling 167 guns) and over 2,000 troops to the area, including some Royal Marines.

As tempers flared on the border, President Buchanan finally received word of the crisis. Shocked, he sent a message to Harney admonishing him for his belligerent actions and stating that this was not a situation that warranted military action. He also despatched Winfield Scott to take command of the U.S. forces in the area and remove the troops from San Juan island.

Scott met with Harney, Pickett and Governor Douglas, negotiating a joint occupation of the island. He also reduced the American military presence on the island to one company of infantry. Douglas agreed, on the stipulation that Pickett not be left in command of that post. Surprisingly, nothing was said about Harney, and he was left in charge of his command, much to the consternation of Scott. 

Harney was not happy with the arrangement, and insubordinately ordered Pickett and his company back to the island in April of 1860. The British protested and once again the situation was cleared up, this time with Harney being stripped of his command.

Nothing more was said about the island until the U.S. and Great Britain appealed to Kaiser Wilhelm I of Germany to arbitrate. In October of 1872, the Kaiser ruled that the islands were south of the 49th parallel, and thus belonged to the United States. The British withdrew their marines a month later.