The Treaty of Ghent, signed by the United States and Great Britain on Christmas Eve, 1814, ended the War of 1812. Because the two countries were so similar in terms of their military strength, the treaty essentially ended the war in a draw. Each country agreed to return to the same conditions that existed before the war, including territorial possessions. The primary issue that initiated the conflict, British impressments of American citizens into the British armed forces, essentially became moot as the Napoleonic Wars ended and Great Britain suddenly had a surplus of soldiers.

The Treaty of Ghent is important to the Columbia River Basin because it led to the restoration of Astoria to the United States, despite British arguments that the post had been purchased by the North West Company in 1813 and thus was British and not subject to the terms of treaty. Americans argued that the purchase, essentially, had been forced. The treaty also re-established the border between the two countries at the 49th parallel. The treaty did not, however, settle the matter of sovereignty in the Northwest.

Both countries claimed to have discovered the Columbia River in the same year, 1792, and both claimed sovereignty to the surrounding country. In July 1815 President James Monroe notified the British that Astoria should be restored to America under terms of the treaty. It was two years before the countries gave the matter serious attention, as they had more important things to discuss in the wake of the war. Reluctantly, the British agreed to return possession of Astoria, but they did not agree to relinquish sovereignty. An American Navy sloop was ordered to Astoria to take possession of both shores of the Columbia; a British Naval vessel arrived two months later to take down the British flag. Thus the Americans claimed possession and sovereignty. Great Britain, however, recognized an American right equal to their own under the treaty, but not exclusive American sovereignty. The North West Company continued to occupy Fort George, with the permission of America.

In 1818, a series of eight conferences were conducted to discuss the issue. The British commissioners said they would accept the 49th parallel as the border as long as the two countries shared possession of the mouth of the Columbia. The Americans refused to recognize any British claims of possession south of the 49th parallel. The impasse was settled by an agreement, called the Convention of 1818, in which the countries agreed to jointly possess the country south of the 49th parallel for a period of 10 years.

The agreement was extended twice, and joint occupancy continued through the era of the fur trade in the Northwest. The sovereignty issue finally was decided in the Treaty of Oregon in 1846, in which the countries established the international border at the 49th parallel. The country north of the line became British, and the country south of the line became American.