The Webster–Ashburton Treaty is signed, establishing the United States–Canada border east of the Rocky Mountains.

The Webster–Ashburton Treaty was a treaty that resolved several border issues between the United States and the British North American colonies. Negotiated in the US federal capital city of Washington, DC, it was signed August 9, 1842, under the new administration of US President John Tyler, who as the former vice president, had just recently succeeded and became chief executive upon the unexpected death of his running mate and predecessor, William Henry Harrison, who had only served a single month in office. The Daniel Webster–Lord Ashburton negotiations and the newly drawn-up 1842 treaty resolved many of the issues arising from the recent border conflicts and skirmishes between Americans and New Brunswickers in the Aroostook War of 1838–1839. It arose from disputes and controversies over the vague indefinite terms and text of the old peace agreement of the Treaty of Paris of 1783, which ended the American Revolutionary War.