The American National Anthem was inspired by the events at the Battle of Baltimore, one of the key moments in the War of 1812. When Francis Scott Key saw the American flag flying above Fort McHenry amidst the cannon fire, he was inspired to write the historic poem "Defence of Fort McHenry". This poem would be put to music to become "The Star-Spangled Banner". The song became the official American National Anthem on March 3, 1931.
Today, you can view the original poem at the Maryland Historical Society, tour the grounds of Fort McHenry, and visit the Star-Spangled Banner Flag House, the home of Mary Pickersgill who sewed the huge flag that flew above Fort McHenry.