The Webster–Ashburton Treaty of 1842 established the final boundary between the countries, giving most of the disputed area to Maine while preserving an overland connection between Lower Canada and the Maritime colonies.

The Treaty of Paris (1783) ended the Revolutionary War but did not clearly determine the boundary between British North America (Quebec and New Brunswick) and the United States.

As late as September 1825, Maine and Massachusetts land agents issued deeds, sold timber permits, took censuses, and recorded births, deaths, and marriages in the contested area of the Saint John River valley and its tributaries.

Massachusetts land agent George Coffin recorded in his journal during one such journey during autumn 1825, returning from the Upper Saint John and Madawaska area to Fredericton, New Brunswick, that a thunderstorm had ignited a forest fire.

During 1826–1830, provincial timber interests also settled the west bank of the Saint John river and its tributaries, and British families built homes in Woodstock, Tobique, and Grand Falls, New Brunswick.

The population of the area swelled with outsiders, however, when winter freed lumbermen from farm work to "long-pole" up the Saint John River to the valley.

These migrant seasonal lumbermen caused particular tension for the governments of Maine and Massachusetts, responsible for the protection of resources and revenues of their respective states.

[3] In preparation for a United States census in 1830, the Maine Legislature sent John Deane and Edward James to the disputed area to document the numbers of inhabitants and to assess the extent of what they considered to be British trespass.

Acting on advice from Penobscot County, Maine, officials, they called a meeting to select representatives preparatory to incorporating Madawaska as a town.

It is morally certain that the intention then was to re-enact the boundary line of the Proclamation of 1763, and that the British argument based on the difference between the Bay of Fundy and the Atlantic Ocean was simply an ingenious quibble.

[4] Both American and New Brunswick lumberjacks cut timber in the disputed territory during the winter of 1838–1839, according to reports submitted to the Maine Legislature, resulting in the Battle of Caribou and other conflicts.

Arriving at T10 R5 (now Masardis), the posse established a camp at the junction of Saint Croix Stream and the Aroostook River and began confiscating New Brunswick lumbering equipment, and sending any lumbermen caught and arrested back to Maine for trial.

Terming the Americans "political prisoners", Sir John Harvey sent correspondence to Washington, D.C., that he lacked the authority to act on the arrests without instructions from London, which he awaited.

On 15 February 1839, the Maine Legislature authorized militia Major General Isaac Hodsdon to lead 1,000 additional volunteers to augment the posse then on the upper Aroostook River.

During Congressional debates in Washington on 2 March 1839, Representative Francis Ormand Jonathan Smith of Maine outlined the events and the various communications sent and received since 1825.

President Martin Van Buren assigned Brigadier General Winfield Scott, then involved in the Cherokee removal, to the conflict area; he arrived in Boston in early March 1839.

[8] Major R. M. Kirby commanded of Hancock Barracks post near Houlton, Maine, with three companies of the United States 1st Artillery Regiment.

Four companies of the British 11th Regiment marched to the area from Quebec City to represent Canada with the intent to build a suitable barracks across the Saint John River from Fort Kent.

However, reports of collusion resulted in the Maine Executive Council assigning Alphus Lyons to investigate Sheriff Packard and District Attorney Tabor.

The British retained the northern area of the disputed territory, including the Halifax Road with its year-round overland military communications between the Province of Canada and Nova Scotia.

Webster used a map that American Jared Sparks found in the Paris Archives while searching for pro-American evidence, which Benjamin Franklin had supposedly marked with a red line, to persuade Maine and Massachusetts to accept the agreement.

Webster replied to later criticism for hiding the map, "I did not think it a very urgent duty to go to Lord Ashburton and tell him that I had found a bit of doubtful evidence in Paris."

The British Foreign Office, without Ashburton's knowledge, acted similarly by hiding the "Mitchell's map", which generally supported the American case.