Britain v. America, fought 1812–1815.
Ended by Treaty of Ghent (Jan 1815), but fighting continued several months after that point in several regions. No border changes, in any event. A stalemate, the treaty ratified the pre–War boundaries.
Great Britain had been at war with Napoleonic France since 1793, and consequently aggressively attempted to restrict American trade with France, and, as well, had a habit of impressing (seizing) American seamen (although many were, indeed, British deserters) for service with Her Majesty’s Navy against France.
With the British defeat of Napoleon in 1814, the above encroachments ceased, and, although Britain now had more forces to send to the Americas, the stage was set for an armistice.
America had made moves on Canadian territory, but was rebuffed militarily.
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Amateur poet American Francis Scott Key witnesses the bombardment by British ships in Chesapeake Bay of US Fort McHenry (Baltimore, Maryland), and composes the lyrics for the Star Spangled Banner, to be combined with a popular tavern melody to eventually, 117 years later in 1931, become America’s national anthem, supplanting both the song “Hail Columbia.” (1789) and the patriotic song (also by Francis Scott Key) “My Country ‘Tis of Thee” (1831).
– after Wikipedia