The Meeting of the Armies in January 1817 was the meeting of the two British armies in the city of New Orleans. The first army had been in the city, protecting it, since the Battle of New Orleans in January 1815, two years previously. The second army had conquered all of the United States of America since landing in Montreal in July 1815. This brought an end to the War of 1812 in the eyes of the British, though some historians believe that the war did not truly end until the British had fully cemented their control in September 1817.
The army occupying New Orleans was commanded by Edward Pakenham, and the conquering army was commanded by Arthur Wellesley. Coincidentally, these two men were brothers-in-law, as Wellesley married Pakenham's sister.