The ostensible reason given for the American declaration of war on Great Britain was the impressment of American sailors to serve on British ships. This occurred at a time when the Franco-British wars were at their height and, although Americans professed to be neutral, had engaged in commerce with both sides. Britain claimed that a number of British sailors had jumped ship in American ports and were now serving on American vessels. They did not bother to verify the nationality of those "pressed" into service; and it is entirely likely that some innocent Americans were forced to fight on British war ships.
A secondary (and important) reason was the desire by a number of members of Congress to see the United States expand its territorial possessions into Canada. These so-called "war hawks," primarily John C. Calhoun of South Carolina, Henry Clay and Richard M. Johnson of Kentucky and, Felix Grundy of Tennessee claimed war was necessary to defend the "national honor." They were characterized as "war hawks" by Sen. John Randolph who said of them:
We have heard but one word—like the whippoorwill, but one eternal monotonous tone: "Canada! Canada! Canada!
The war itself did not go well for the Americans. After the defeat of Napoleon at Waterloo, the British were able to devote their full attention and resources to the war. At its conclusion they had captured Washington D.C. and President Madison had been forced to flee. The Treaty of Ghent, which ended the war, never mentioned the issue of impressment which had sparked the war. There were two important consequences, however. Gen. Andrew Jackson's victory at New Orleans propelled him into national prominence which eventually led to his election as President. Also, the war itself engendered a tremendous spirit of national pride. The end result was a briefly united nation during the "Era of Good Feelings."