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In the OTL, on June 15, 1859 an American settler in the Oregon territory inadvertently nearly sparked a war between the British and America when he shot a pig on San Juan Island.

According to Wiki:
On June 15, 1859, exactly thirteen years after the adoption of the Oregon Treaty, the ambiguity led to direct conflict. Lyman Cutlar, an American farmer who had moved onto the island claiming rights to live there under the Donation Land Claim Act, found a large black pig rooting in his garden.[2][5][7] He had found the pig eating his tubers. This was not the first occurrence. Cutlar was so upset that he took aim and shot the pig, killing it. It turned out that the pig was owned by an Irishman, Charles Griffin, who was employed by the Hudson's Bay Company to run the sheep ranch.[2][5][7] He also owned several pigs which he allowed to roam freely. The two had lived in peace until this incident. Cutlar offered $10 to Griffin to compensate for the pig, but Griffin was unsatisfied with this offer and demanded $100. Following this reply, Cutlar believed he should not have to pay for the pig because the pig had been trespassing on his land. (A possibly apocryphal story claims Cutlar said to Griffin, "It was eating my potatoes." Griffin replied, "It is up to you to keep your potatoes out of my pig."[7]) When British authorities threatened to arrest Cutlar, American settlers called for military protection.

The initial military response was the dispatch of 66 soliders of the 9th Regiment under the command of then Captain George Pickett.

Again, according to Wiki:

By August 10, 1859, 461 Americans with 14 cannons under Colonel Silas Casey were opposed by five British warships mounting 70 guns and carrying 2,140 men.

and

The governor of the Colony of Vancouver Island, James Douglas, ordered British Rear Admiral Robert L. Baynes to land marines on San Juan Island and engage the American soldiers under the command of Brigadier-General Harney. (Harney's forces had occupied the island since July 27, 1859.) Baynes refused, deciding that "two great nations in a war over a squabble about a pig" was foolish.[5][7] Local commanding officers on both sides had been given essentially the same orders: defend yourselves, but absolutely do not fire the first shot. For several days, the British and U.S. soldiers exchanged insults, each side attempting to goad the others into firing the first shot, but discipline held on both sides, and thus no shots were fired.

What if, however, much like the Shot Heard 'Round the World, an anonymous soldier had fired and opened a skirmish. In this case, Captain Pickett, who gained national fame for his actions at the Battle of Chapultepec in the Mexican-American War is mortally wounded during the initial skirmish?

Both sides, of course, claim that the other side fired the initial shot but there is no way to prove conclusively which side is responsible.

Given the extremely tense climate between the Northern and Southern states by mid-1859, what impacts (if any) would a shooting war with Britain in the northwest have on the brewing American Civil War?
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