The Aroostook War was not really a war. It was a tense conflict between Maine and New Brunswick about the proper border between the United States and Canada in the area along the Aroostook River. In 1839, the Maine legislature sent militia to the river to remove what it perceived to be Canadian interlopers. The New Brunswick lieutenant governor, Sir John Harvey, issued an order to remove Americans from what he believed to be Canadian, and thus British, land.

Van Buren dispatched General Winfield Scott to work out a compromise. Eventually, both countries signed the Ashburton-Webster treaty of 1842 that set out the exact borders between Maine and Canada.