In 1859 therewere about 25 Americans on San Juan Island. They were settled on redemption claims which they expected the U.S. Government to recognizeas valid, but which the British considered illegal. Neither side recognized the authority of the other.  Tempers were short and it would take little to produce a crisis. 

That crisis came on June 15, 1859, when an American settler named Lyman Cutlar shot and killed a pig belonging to the Hudson's Bay Company, because it was rooting in his garden. When British authorities threatened to arrest Cutlar, American citizens drew up a petition requesting U.S. military protection. Brigadier General William S. Harney, the anti-British commander of the Departmentof Oregon, responded by sending a company of the 9th U.S. Infantry to San Juan Island. The 66 man unit landed on July 27 and occupied a commanding spot near the Hudson's Bay Company wharf, just north of Belle Vue Farm. 

James Douglas, governor of the new Crown colony of British Columbia, was angered at the presence of American soldiers on San Juan Island. He had three British warships under Captain Geoffrey Hornby sent to dislodge Pickett, but with instructions to avoid an armed clash if possible. Pickett, though over whelmingly out numbered, refused to withdraw.

Mean time, Pickett had been reinforced on August 10, by 155 men under Lieutenant Colonel Silas Casey, who now assumed active command. This meager force still seemed inadequate to face the growing concentration of British vessels and men, so Harney ordered in additional reinforcements. By August 31, 461 Americans, protected by 14 cannons were opposed by five British warships mounting 167 guns and carrying 2,140 troops, including Royal Marines, artillery men, sappers, and miners.