This is coolbert:
The state of Maine USA versus the British Empire? Almost.
The Aroostook War.
Only the most vaguest terms possible was I familiar with this incident. Incident as best characterized.
"The Aroostook War (sometimes called the Pork and Beans War was a military and civilian-involved confrontation in 1838–1839 between the United States [militia of the state of Maine and not federal U.S. troops involved] and the United Kingdom over the international boundary between the British colony of New Brunswick and the U.S. state of Maine. Several British were captured; no one was killed, but two Canadian militia were injured by U.S. Army troops [Maine militia?] prior to the diplomatic compromise . . . The term 'war' was rhetorical; local militia units were called out but never engaged in significant combat. The event is best described as an international incident."
CONSEQUENCES OF THE "WAR" HOWEVER MORE LONG-LASTING AND PROFOUND THAN THE INCIDENT ITSELF!
"Despite the lack of military action the episode had major consequences on the states' right to use military force on their own with the understanding that the main purpose was to address internal conflicts. In the aftermath of the crisis, the Federal government assumed complete control over military matters. The episode was to be the last serious confrontation between the US and the United Kingdom."
NO STATE ALLOWED TO FIGHT A WAR AGAINST A FOREIGN POWER! PERIOD!
See also the "54° 40' or Fight" crisis of 1846. The United States and Great Britain continuing to be at loggerheads.