Indians, criminals, and game crossed the Canadian boundary at will, streams flowed across it, and the coast cities vied for the trade of the interior, indifferent to the claims of national allegiance.

One cannot but believe that this intimacy has in the long run made for friendship and peace; but it has also meant constant controversy, often pressed to the verge of war by the pertinacious insistence of both nations on their full rights as they saw them.
The fifteen years following Adams's encounter with Canning saw the gradual accumulation of a number of such disputes, which made the situation in 1840 exceptionally critical.

Great Britain was angered at the failure of the United States to grant her the right to police the seas for the suppression of the slave trade, while the United States, with memories of the vicious English practice of impressment before the War of 1812, distrusted the motives of Great Britain in asking for this right.

Nearly every mile of the joint boundary in North America was in dispute, owing to the vagueness of treaty descriptions or to the errors of surveyors.

Twelve thousand square miles and a costly American fort were involved; arbitration had failed; rival camps of lumberjacks daily imperiled peace; and both the Maine Legislature and the National Congress had voted money for defense.